I think I'll be getting started on my Zenith L1846R sometime soon, so I've been sorting out the parts list I'll need to put together. I already have a good list of all the capacitors that are gonna have to go, but while I was at it, I went ahead and checked around on the resistors, too. Among other things...

Here's one thing that I decided to get out of the way early:

http://img830.imageshack.us/img830/7654/img0166at.jpg

The original plastic cover over the yoke had deteriorated and created a mess of black shards that I'm still finding all over the place. Testing those resistors was getting pretty boring, so one night I decided to make a cover myself. It's just a bunch of thin card-stock type paper from a folder rolled up, cut, trimmed, and coated in duct and electrical tape. It holds my magnetic rings nicely, but I'll want to go back and seal this thing over with something heat-resistant. Plastic coat and engine paint should work.

A fellow told me that he remembered these sets having faulty screen resistors near the horizontal output tube. I found a bunch of resistors going from pin to pin that aren't listed in my schematics:

http://img831.imageshack.us/img831/1228/img0171q.jpg

I found one resistor in the parts list that was called a "screen resistor." It was a 200 ohm resistor. It's way over by the tuner stuff, though. There's another near the horizontal output tube that looks similar but I haven't figured it out yet:

http://img836.imageshack.us/img836/6324/img0168i.jpg

Both those read very little resistance.

Here's something else I haven't seen before:

http://img825.imageshack.us/img825/3006/img0173c.jpg

Schematic calls it an "integrator." Looks just like a ceramic cap with three leads.

I also noticed that the getter on my horizontal output tube looks a little hazy...

http://img839.imageshack.us/img839/6708/img0180u.jpg

And now, something I really need some advice on: My flyback!

http://img835.imageshack.us/img835/2546/img0181l.jpg

Looks kinda grody. Doesn't help much that it was right in the path of those falling chunks of plastic from the yoke cover. This is the first time I've popped the cover off the top of the high-voltage cage. I only managed to clean up around the 1B3 before because I could reach it from the back and it was covered in smut. But, the flyback itself is surrounded in filth and seems to have a coat of wax peeling off, which you can see there in the picture. I've read that getting dirty and falling apart like that can lead to serious problems. I hope there's something I can do to clean it up and keep it in one piece!

That resistor with the coil around it will check really low, you are measuring the coil mostly and not the resistor.

The black things with the color bands are capacitors, Black Beauties, Bumblebees, whatever you call them, they need to be replaced.

I wouldn't worry about the integrator or the resistors at this point, I would recap first then check resistors if you have any issues.

The flyback needs to be re coated with something, most Zenith Flys seem to be cracking and flaking even when they work OK.

I'd probably clean off that old wax and then coat it with Low Acid Silicone Rubber. You have to be very careful not to break off any of the very fine wires while you're doing it of course.

This stuff here works good for insulating too:
http://www.aervoe.com/paints_coatings/Insulating-Epoxy-Coating.html

Thanks for the advice on the flyback! Yeah, I need to figure out how to get this out of there safely so I can clean it up. It's only got two screws that hold this assembly under the chassis, but past that there's just the wires leading to it. They go through some tight rubber fittings and have to be pulled through partway just to get the flyback loose from underneath but it only comes out so far. I'm not sure of a good way to undo those wires other than unsoldering them from the flyback, which seems iffy since I'd have to get a soldering iron so close to all that wax.

I'll find a way to get to this so I can clean it up and coat it. I presume this flyback was fine. I was able to get a perfectly squared image that filled up the screen before, but there was no sync any which way. Also no sound.

But yeah, I just was poking around through these resistors in the meantime because I knew I'd have to place another order again later if any were bad so I wanted to see if there was anything that stuck out to me in advance. So far, only two that seem to be out of spec. I did find an annoying number of bumblebee's in there. In total, I think I have about 37 caps to replace.

First, as I go about ordering the electrolytic caps, I noticed that a few of the value's I need for this set are out of stock. I can order the same value of the next available higher voltage rating, or exceed the value without having to go up and thus save a bit on price. I've read that it's safe to exceed the capacitance value in radios, so is that still fair game in a television set like this?

Also, where do I find a power cord? Simple issue; replace cord. But, I really, seriously, have no idea where to get one for my television. It's a simple brown cord, non-polarized blades, and the end that goes to the set has a plastic piece with two female ends ( like what some call a figure-8 ) and it has tabs with holes as if to use screws or rivets on either side. My cord wasn't screwed or revetted, but simply flopping around in an interlock. Don't like it.

http://img838.imageshack.us/img838/2773/img0194v.jpg

It's stuck in there, so I guess I'll have to drill the rivets that hold the interlock together to the back cover, but I still don't know where to find a proper cord. I've tried searching for it online, but I don't know what I'm looking for? Not too keen on power cords...

If the cord is in otherwise good condition, don't be concerned about it. It should "float" in it's mounting to help facilitate the installation of the back, and the alignment of all the back's screws while at the same time confirming the mating of the cord to the chassis.

Hopefully, you should have some spare (loose) cords for troubleshooting, otherwise known in the trade as "cheater cords".

If you do need one maybe Moyers or Mock Electronics for starters will have some NOS ones. I've got quite a stash of 'em so I really haven't given it much thought as to where to purchase them anymore...

In the late 50's-early 60's Remington electric razor cords made perfect cheater cords for many TV brands.

The original cord is partially cut in half. I had it patched up just to test it before, but I need a correct replacement, or at least a brown cord that's compatible. I have cords that will work crudely for testing, but I don't want to be stuck with any of those as a final solution. So, I'm just keeping my eyes out for a NOS or at least something close. I'm not picky about originality, just appearance. The old cord didn't even say "Zenith" on it. Just "Phalo, USA" whoever that was.

I've read that it's safe to exceed the capacitance value in radios, so is that still fair game in a television set like this?
Using the next higher value should not be a problem. For instance, substituting 33uf for 22 uf is OK. The higher value may be a little larger physically. I would not go more than twice the spec'd value. Check the B+ voltage after you're done recapping to make sure it's within reason. A little higher than spec'd is OK (pretty common, actually, since line voltages are somewhat higher now).

Phil Nelson

Alrighty. Well, I couldn't find a 40uF in a voltage rating I needed, so I went up to a 47uF in those cases. Oddly enough, I found a 4uF rated at 550v in my parts list, but in the schematics, the circuit legend, and in the television itself on the cans, the corresponding filter cap was actually labeled as 4uF at 350v. I guess it was a typo. It made the difference between a $1 cap versus a $4 one, so I'm glad I noticed it.

I started recapping the set yesterday and I got a good bit more done today. Nothing but a couple bumblebee's and the electrolytics left. I noticed that one of these 47uF's I've got will replace a 40uF that appears to be first in line to the 5U4G low voltage rectifier. I recall hearing that exceeding the original capacitance rating of filter capacitors closest to the rectifier could overdraw the rectifier during the start-up surge. The 47uF's are all I could find, and it's only 15% off. Cause for concern? Just thought I'd get a second opinion on this.

It won't matter. You'd have to be off by a huge amount. 15% is still smaller than the normal tolerance of electrolytics.

John

Ah, well that's good. I had figured as much, but I thought I'd make sure. I've replaced about 26 capacitors so far, so I've got less than a dozen left. It's getting close to that time... about to find out if she glows or blows. :D

UPDATE:

http://img810.imageshack.us/img810/2470/img0324b.jpg

Almost there... 5 more electrolytics and a couple hard-to-reach capacitors still left to go.

I finished recapping my Zenith tonight and was ready to test it out with the new CRT, but I now have reason to suspect that the rebuilt CRT I bought awhile back isn't really a 17LP4. While it does look nearly identical to the original, I'm having problems getting it to fit in the cabinet properly. I've managed to get it inside, but it looks "different" once you get it in there. I can see the edge of the black frame that supports the CRT more than before, and it looks higher up with more of a gap at the bottom. Worse still, is the fact that the shafts of the switches don't stick out as far as before, and I can't even get my power/volume knob on far enough to keep it in place.

I don't know what to do, honestly. I've been working on this all night, and I'm exhausted. I've pulled that chassis out 3 times so far, and I still can't get it right. Guess I'll try and figure it out tomorrow...

http://img821.imageshack.us/img821/7025/img0332hb.jpg

http://img837.imageshack.us/img837/6609/img0335w.jpg

It's possible that your rebuild started life as a different tube #. These early square crts went through a few changes in geometry as they went through various manufacturing changes.

I know my 17" Sentinel is a real pain to get back in the cabinet, showing the exact same symptoms you describe. I just really have to mess with it to get the mask to line up right, or else the controls won't stick out far enough.

Right now, though, I would just focus on seeing that your tv is working before fussing over this setback.

Yeah, I was putting off my initial testing due to the fact that I was too tired to fool with it, and I was hoping to tuck the chassis back in the cabinet to clear up some of the clutter I've accumulated working on all of this. I'm excited to see how it's gonna work, but I never did even test fit this new CRT when I got it so I wanted to make sure it would work out. Looking back into it today, I should have no problem. Even putting the old CRT back in renders the same symptoms so I know it's probably a minor adjustment that I've overlooked. If the tube is in fact that much longer, the yoke can be adjusted from front to back about a half of an inch. So, I'll keep that in mind.

Alright, here's what the tentative end result of my recap looks like: I say tentative because there's a couple more I could replace if need be.

http://img299.imageshack.us/img299/2653/img0329j.jpg

Hey leadlike, I remember asking you about that 2 x .01 ceramic and I do have two .01's to replace it but I haven't yet, because it didn't seem to be open or shorted and it was pretty hard to get to. I still may replace it anyway, though. There was also a .001 ceramic? that I couldn't find. Either way, my sound isn't working, just as I figured would happen. ( But I'll explain that later )

First off, I did get it to fit in the cabinet. I scooted the yoke back just a hair and that helped somewhat:

http://img33.imageshack.us/img33/8466/img0334wk.jpg

http://img46.imageshack.us/img46/7352/img0343f.jpg

Haven't gotten around to painting that control panel gold yet, but it should look nice when it's done.

Anyways, I finally fired it up with the new CRT and all the new capacitors and was treated to some static and pops from the speaker. I had the volume all the way down, but the noise cracked in and out for about 15 seconds or so and finally went away completely. I thought maybe the volume switch had an issue, but I fear it's actually the audio output transformer. There's a small burn on it that I had noticed before. Keep in mind, I haven't changed any tubes, either and I'm pretty sure that's going to be next on my agenda.

As for the picture... well, I've got something!

http://img830.imageshack.us/img830/3712/img0340a.jpg

No need to worry about ion burn. Looks like it's already got one on the center of the screen. Very small and faint, though.

http://img243.imageshack.us/img243/3378/img0341h.jpg

I recall bandersen having issues with dark vertical lines on the Motorola he's been restoring, which I believe had something to do with the flyback? I seem to have very faint vertical lines, but brighter rather than darker. Huh... no concern, there.

I can't get the vertical and horizontal to sync up into a watchable image, but I haven't had very long to play with it so. I'm not familiar with the proper technique for adjusting these things from scratch. I'm willing to bet there's a couple tubes that could use replacing, too. Using a VCR as input, I can tell from the changes in brightness that it's getting the signal at least.

So, no sound, bright raster, nothing watchable. But... it feels like progress.

Definitely progress :)

I have a burn like that on a couple sets. I think it's from the bright dot that forms when the set is turned off. I recall someone came up with a circuit to cut the beam off immediately.

If you have a horizontal drive control, adjusting that may reduce those lines. It certainly helped with the Motorola although doing so reduced the overall brightness.

You know, I thought the same thing about the tiny ion burn. Since my old CRT was so weak, the few times I tried it out, I never saw that little tiny white dot after I turned the set off. This time, I did. It was off-center, down and to the left of the old burn. I think I need to turn my yoke slightly counter-clockwise and maybe fiddle with the centering magnets.

I'll try that "hor drive" control later and see how it changes things. Mine is on the back, along with a fringe lock and buzz control. There's also a bulls-eye adjustment but that had something to do with the tuner.

I remember you saying once how unnerving that first power-up can be after doing major work, and boy was I feeling it today! I've only replaced capacitors in two old radios so far, and I'm still pretty new to it. In the case of this Zenith, I've replaced almost 40 components so far, including all of the electrolytics. Since I had already ordered axial caps, I decided I wouldn't attempt to re-stuff the old cans and instead simply install the capacitors under the chassis. Figuring out how and where to position these capacitors made my brain hurt, but I'm pleased with the result. I feel that the resulting layout doesn't look too shabby, and thankfully... nothing popped, crackled, or smoked. Maybe I'm getting better at this. :scratch2:

Hey! Almost there. I don't think you'll notice the burn once you get a picture.

Good work.

John

that is VERY encouraging! Take some measurements on your audio output transformer to confirm it is toast. I should have a spare one I could pull from a junker chassis for you.

But for now, hook up a video source and see what kind of picture you get....

Thanks for the encouragement, guys! I've been using a VCR as input and I thought I'd get something on channel 3 or 4, but 4 goes black the moment I turn on the VCR. I was getting something to happen on channel 6, so I went with that...? :dunno:

I had Rio Bravo playing on the VCR and finally got this:

http://img802.imageshack.us/img802/4545/img0348.jpg

http://img512.imageshack.us/img512/2642/img0350k.jpg

Wow, John Wayne and Dean Martin are actually recognizable through that mess! I couldn't get the picture to stop overlapping from top to bottom. I did finally get the horizontal to lock and the vertical to more or less stay in place. Horizontally it would jiggle just slightly here and there, and vertically it would roll here and there and sometimes it would go dark and flip out and I'd have to readjust a few things again. I can't get it too bright without being washed out.

By the way, here's what that audio output transformer looks like:

http://img18.imageshack.us/img18/2507/img0314pg.jpg

I took this picture while I was recapping. You can see the burn mark pretty clearly. The schematic has readings for this transformer but they're printed really small. I think it says .5 Ohms on the "out" side and either 380 or 580 Ohms on the other side. I did check for the .5 Ohms and I got more like .004 or something, shorted I guess. I'll have to take a closer look at it next time I pull out the chassis. I wonder why it crackled for a bit and gave up. Arching inside the windings? It did this the first time I ever turned on this tv, but to a much lesser degree. This time it actually sputtered quite a bit before it gave up. Hasn't made a sound since.

VCRs are just about the worst video source-I had a tv set that was giving me vertical troubles last week, only to find that it was just the tape I was playing. Once I changed tapes, the problem stopped. VCRs can also create weird smearing effects at the top of the picture and all sorts of other fun things. Before you do anything else, get a DVD player or use your cablebox for a video source. Not sure what to tell you about the signal coming through on channel 6, though...

If your picture is locking on vertical that way, with a "stable" double image, something is making your oscillator run off frequency. It is a pretty common problem, so some voltage checks from the sync separator to yourt vertical output will hopefully find the problem.

The burnt output transformer might have been caused by running the set with bad caps, or maybe something got miswired-definitely check for that possiblity before putting a new one in.

I did a little more tinkering with the set this morning and found that I could get a surprisingly stable picture despite the overlapping image which I'm still looking into. The contrast and brightness isn't too impressive, either. Turning the contrast, brightest, and screen register all seem to do the same thing. They just wash out the image. In any case, I only ordered two resistors that I was pretty sure needed to be replaced from looking over it before, but these were mainly in the horizontal section. There appears to be a couple of 10% resistors that are out of spec, especially a 680k that measures more like 40k if even that. Unfortunately, I ordered only what I thought I needed and I have no replacements on hand. If "Sync Clip" and "sync separator" mean the same thing, I think I'm looking in the right places.

I've been meaning to take some voltage readings in this area, but I wanted to ask about leaving the high voltage out of it. I don't think I need to run the CRT at HV to take those measurements, and I was hoping it would be safe to pull the 1B3 or something to that affect. I just wanted to make sure first. Discharging the CRT seems to be no challenge at least. It doesn't spark near as much as I'd feared.

Now here's something I found:

http://img821.imageshack.us/img821/1278/img0363d.jpg

On the left, the original audio output transformer and to the right is one I pulled from a derelict RCA radio chassis ( Model 8R74 ). The schematics for my set say that the AOT should measure 580 ohms across the "in" side, and .5 ohms on the "out" side. The one I pulled out measures (?) million ohms across the "in" and .8 across the "out" and is clearly burnt. I can't find any faults in the wiring. It was burnt when I got it, judging by pictures I took then, so I'd say it was the bad capacitors.

Now this other AOT worked in the other radio and measures .5 "out" and has 3 wires on the "in" side. There's a green, a striped red and white, and a red. Green to striped, it's 582, green to red it's 595, striped to red is 14. As best I can tell, that striped wire went to the rectifier of the radio. What I'm wondering is since the resistances seem to coincide closely enough. could I use this transformer and omit the extra wire somehow or another?

The resistance isn't as important as the turns ratio. However having said that, it'll probably work well enough. I'd use green to red and leave out striped one disconnected.

John

Well, I had to do some serious work to get it installed, but it's finally in. I left out the striped wire and went with the green and red. It was a pain to install, mainly because the bracket around the AOT had to be swapped with the other in order to fit properly and even then, the holes in the bracket had to be drilled out a bit in order for the screw holes to line up. It's because the bracket was forced into being a bit wider than before, fitting around a transformer that is literally less than a millimeter larger in width.

I put everything back together and fixed my pilot light while I was at it. Someone had a #47 in there but the bulb was too long to line up with the "window" it had to shine through in order to project the number. I swapped it for a #44 and it now works great!

As for the sound...

It works but it's VERY buzzy. All of the cable channels come through with a lot of loud buzz and distortion that overpowers everything. The buzz gets louder when the picture gets brighter. The VCR fairs a little better, but the buzz is still obnoxious. Plenty of volume... the tone control works nicely... but the noise is horrible. I tried adjusting the "buzz control" on the back and it only made it louder. :thumbsdn:

UPDATE:

I can get the buzz to go away with the VCR playing by turning the screen register up and tweaking the fine tuning and buzz control. This only works with the VCR, though. The cable channels still sound distorted beyond belief. I guess it's something about the raw cable signal. I don't have a converter box, just the VCR. I'd try the DVD but the only DVD player I have uses the red, white, and yellow connectors. This tv came with a coaxial adapter so I've been using anything that plugs in that way.

As for the sound...

It works but it's VERY buzzy. All of the cable channels come through with a lot of loud buzz and distortion that overpowers everything. The buzz gets louder when the picture gets brighter. The VCR fairs a little better, but the buzz is still obnoxious. Plenty of volume... the tone control works nicely... but the noise is horrible. I tried adjusting the "buzz control" on the back and it only made it louder. :thumbsdn:

UPDATE:

I can get the buzz to go away with the VCR playing by turning the screen register up and tweaking the fine tuning and buzz control. This only works with the VCR, though. The cable channels still sound distorted beyond belief. I guess it's something about the raw cable signal. I don't have a converter box, just the VCR. I'd try the DVD but the only DVD player I have uses the red, white, and yellow connectors. This tv came with a coaxial adapter so I've been using anything that plugs in that way.

The buzz is caused by the sound carrier being turned off by the video peaks at white in the picture. White in the video image coincides with minimum TV channel carrier, and if an IF amp is misbiased, the carrier can momentarily disappear. Most TV sets use an "intercarrier" sound IF system. As TV sound is on an RF FM signal 4.5MHz above the picture carrier, it shows up at the video demodulator as an FM signal at 4.5MHz. But if the picture carrier disappears so does the 4.5MHz FM sound signal. This disappearance ends up sounding like a buzz, as the peak white details in the video image repeat at the vertical rate, 60Hz.

So there may be a weak tube, bad resistor or such in the IF strip. The audio amp is likely not a fault. But sometimes some TVs used the audio output circuit as an IF strip voltage source, they'd place the audio output circuit in series with the bank of tubes in the IF strip. But your TV probably doesn't do that, else you would have gotten no reception with the open primary of the audio output transformer.

I see what you're saying. That's interesting... I'd always wondered what it was about bright images that would make that little buzz come through the speaker on some of televisions I've watched over the years. I'd never heard it this bad before, though! My dad even told me that he remembered a lot of televisions that buzzed back then.

I'm poking around in the IF section and checking resistors. For many of them, it's hard to say if they're good or bad since they have both ends going to ground or a coil so that they read shorted. So far, most of the one's I can get a reading on appear to be good. As for the tubes themselves, it uses 3 6CB6's. Of them, one is a red-lettered Zenith brand and likely original to the set. It looks a little cloudy in the upper half unlike the other two, so getting a few NOS 6CB6's wouldn't hurt. I'd love to be able to plug these tubes into a tester and get a simple "good" or "bad" but I can't get ahold of a tube tester to save my life. I watch them on Ebay all the time. Even old, untested emissions testers are selling for far more than they're worth, in my opinion.

In regards to my overlapping vertical troubles, I did find a 680k resistor coming off the 6BE6 (sync clip) that read's more like 40k or less. There's a couple others than are "iffy" but likely not a problem. They're on the borderline of their listed tolerance. I also found out why I was getting the VCR on channel 6. When I took the tuner out before, I had turned the turret and when I put it back, it was naturally in disagreement with the controls. I took care of that easily enough.

I'm poking around in the IF section and checking resistors. For many of them, it's hard to say if they're good or bad since they have both ends going to ground or a coil so that they read shorted. So far, most of the one's I can get a reading on appear to be good.

Those resistors "shorted" by the coils are likely okay. I was thinking more about if the B+ voltage and AGC voltages are reasonably correct.

The hard to find parts look to be working fine, and it's likely just a matter of finding a few bad caps or resistors.

After replacing several resistors between the sync clipper and vertical oscillator, I found that leadlike's appraisal of my vertical troubles was spot on! That helped ALOT!

http://img204.imageshack.us/img204/6448/img0369hh.jpg

I still need to do some tweaking, but it's starting to look nice! I don't know if you can tell from that picture, but I've been getting a "curve" in the image towards the top of the screen. Everything starts bend off to the right in the top few inches of the picture. I also found some other horizontal jitters...

http://img299.imageshack.us/img299/2497/img0372d.jpg

This is from a Tweety Bird cartoon, btw. Still need to get an RF converter so I can plug in the DVD, which I'd imagine will look better than this. Still, I get the impression there's at least something amiss in my horizontal section. My sound's still buzzy, of course. I've got some new IF tubes on the way that will hopefully help that. My contrast is still pretty weak, too. Any chance that my video amp tube might need replacing? It's a 12BY7.

The bending is probably related to the horizontal sync, so probably fixing one will solve the other. Dig around in that area for bad resistors/weak tubes.

Your screen shots look really dark-does the picture look pretty good as far as brightness and contrast go?

Still need to get an RF converter so I can plug in the DVD, which I'd imagine will look better than this.
A DVD may look better, indeed. There are so many variables with VCRs, not to mention different tapes. I generally have more issues with tapes than DVDs on my old sets. That includes vertical bending, especially near the top.

Phil Nelson

I found that the bending a the top of the screen doesn't occur on the cable channels, so I'm thinking it's definitely the VCR. Also, that double horizontal image only happened with those cartoon tapes. Later I turned the set back on to show a friend, and I didn't get that problem then, either.

As for the brightness and contrast, I can get the screen to become fairly bright by cranking up the brightness... but increasing the contrast virtually does the same thing. It just becomes brighter until everything is barely recognizable. Turning up the screen register does the same, and I've tried various combinations with only a few rather poor compromises. The only way I could get decent contrast was to turn the screen register way down and then turn up the brightness, and the contrast would improve somewhat. However, turning the screen register down increases the buzz so badly that the image begins to jitter horizontally. So, the pictures I took appear fairly dark because I have the picture set to the best compromise between picture and sound.

I have three NOS 6CB6 tubes on the way for the IF section ( GE brand for $1 a piece ) and I'm hoping that might help the buzz at least. I had just read somewhere that a washed-out, low-contrast image was sometimes the result of a bad video amp tube. So, unless there's no truth to this, I might consider picking up another 12BY7.

The picture has improved significantly...

http://img339.imageshack.us/img339/6796/img0374wc.jpg

The bad news is that the new IF amp tubes didn't help. Actually, it seems that when I change channels, the horizontal goes nuts and all the sound goes away, then after about 30 seconds or so, it eventually all suddenly comes back. All the audio is really distorted depending on the channel, and the buzz is still prevalent. I guess I'll get back to hunting through resistors and ceramic caps.

I believe poor alignment can lead to that symptom-where it takes a minute for the picture to sync when you change channels. Your set is really turning out like the first 21" I restored-an RCA tabletop. For the longest time, I just had this faint washed-out picture, but as I replaced more and more bits, it came together.

If you totally ignore the audio (turn it down) and adjust for best picture, is there a combination of picture controls that gives you a nice image? Good contrast, brightness, focus?

Phil Nelson

Also check for open peaking coils. they will give you a washed out picture.

Well, one thing I noticed is that the control I was calling the "screen register" is actually the A.G.C. delay. The A.G.C. isn't labeled on the control panel and it's right next to the screen control, which is unused. It's just an empty hole?

So yeah, I can get better contrast by bringing the A.G.C. delay down ( darker but more contrast ) and turning then turning the brightness up. However, the lower the A.G.C. goes, the louder the buzz, and to a certain point, the horizontal starts to jitter really bad.

Last night, I figured out how to auto-program the VCR and use it as a cable box. The television's tuner may be out of alignment, but at least I can get channel 3 cleanly enough to flip through the channels on the VCR without much trouble. Many channels still need a bit of a tweaking to get the buzz to a moderate level ( fine tuning, buzz control, etc ) to where it's not perfect, but certainly watchable.

Where would these peaking coils be located, if I do indeed have one that's potentially open?

I would also double check the capacitors in the video output circuit for correct value and wiring...it looks to me as if you get a decent black at the edges of a transition to a black area but it does not last, as if there is a cap somewhere in the circuit is too small a value. Does this set have DC restore circuit?
jr

Here's something I was wondering about ever since I recapped my set...

http://img813.imageshack.us/img813/240/img0389.jpg

To mount these two filter capacitors I used the lugs of two of the vertical output tube's unused pin sockets. It was convenient this way because I could still arrange that 470 ohm resistor between them and send them both to a common ground, which is also being shared with a 47uf from the audio output tube. The big 80uF filters from the low voltage rectifier, and the 30uF filters pin 8 of the audio-out. I just thought I'd mention this in case there's a chance that there might be a problem with this arrangement. It concerned me that there might be something about the close proximity of these unrelated tubes/circuits that could cause any of the problems I've had.

None of the capacitors I replaced are of the wrong values. A couple of the 40uF have been replaced with 47uF, which should be fine. If I'm reading this right, however, this .002 should be a .001?

http://img691.imageshack.us/img691/4079/img0393q.jpg

Oh, unless this was the .001 I was looking for...?

http://img180.imageshack.us/img180/5678/img0395q.jpg

There's three red "domino" caps in this set. Never dealt with them before.

Anyways, I was able to watch some tv on my set last night and today with some buzz here and there. If I played old movies from the DVD player, it worked fine. But if I put in something more modern, there were sudden scenes of bright to dark and everything got buzzy. I just pulled the chassis back out again and I found a 100k resistor between the contrast control and the video amp tube that was reading about 40% out of spec, so I replaced that. I'll let you guys know if I find anything else.

Oh, and I'm not sure about the DC restore circuit. I can scan some of the schematics if it would be of any help.

Here's a clip I recorded earlier today after making some adjustments to the yoke and centering rings. I still don't have the contrast I want, and the buzz is still there on some DVD's and the cable channels, but I can certainly tune it out well enough to play these black and white movies!

http://www.youtube.com/watch?v=ofUCT57sfRM

Here's what my Ryder's manual for this set has to say about sound alignment:

"1. Tune in a tone modulated TV signal and adjust the step attenuator until the signal is reduced to a level where "hiss" is heard with the sound.

2. Adjust the sound take-off coil L19 ( top and bottom slugs ), intercarrier coil L22, quadrature coil L2 and buzz control R39 for the cleanest sound and minimum buzz. It must be remembered that any of these adjustments may cause the "hiss" to disappear and fruther reduction of the signal will be necessary so that the "hiss" does not disappear during alignment.

If intercarrier buzz is in evidence, after all normal sound adjustments have been made, the cause may be attributed to one or more of the following:

1. Improper adjustment of the AGC delay control.

2. Defective 6AU6 sound limiter

3. Extremely high signal levels which require attenuation of the antenna circuit.

4. Transmitter over modulation."

I think I should locate these adjustments and have a look at it. The most believable fault here to me would be the 6AU6. I just cant imagine that these adjustments were ever in need of changing from the factory, so I get the impression there is a component failure that's pushed this out of alignment.

The contrast issues are another story...

[QUOTE=RitchieMars;2984260]The picture has improved significantly...


AYEEE! Michael Cogdill on WYFF!!! That set is going to look GREAT!!!

The 6AU6 is not expensive, either.

Lookin' good :thmbsp: I think you're in the homestretch.

AYEEE! Michael Cogdill on WYFF!!!

Yeah, I believe he lives not far from here up in Simpsonville. I've seen him around town a couple times in the past. One time he was at El Jalisco's having dinner, and the other time he was standing next to his car at a red light where someone had apparently rear-ended him!

Its a small world. My sis and brother in law have a place in Simpsonville.

I think you're coming down the home stretch now!

Indeed, my set seems to be finally coming along and I couldn't be more pleased considering where it started from! Based on the suggestions I've heard on here, as well as some insight from various trouble-shooting booklets from the 1950's, I've looked over my schematics and have compiled a checklist of things that might need some attention before I can call it done. Hopefully, a couple tubes and maybe a few more resistors will iron out these deficiencies.

Oh, and I'm not sure about the DC restore circuit. I can scan some of the schematics if it would be of any help.

It might not hurt to scan in the circuits between the last video IF stage and the CRT... perhaps we can spot some potential trouble spots, and the DC restore circuit (if any).

jr

Alrighty, here's a scan showing the last stage of the video section, and the vertical section is visible below it. I left all that in there because the AGC is controlled by half of the 12AX7.

http://img193.imageshack.us/img193/9213/schematicsvideo.jpg

Again, the symptoms include a washed out picture and virtually no contrast when the picture is adjusted to maximize sound output. Turning down the AGC improves contrast somewhat at the cost of sound, and eventually an unstable image. Brightness on the whole is fair, I suppose. It wouldn't look so great in a well-lit room.

comp signal applied at video test point, determine if proble is before or after that point. (pin 2 V6)

That sounds like a good test!

Looking at the circuit, I don't see an obvious DC restore circuit.... I would check again the value and connection of C-33 (.1uf) and also make sure that r-33 is the correct value as well.

L-20 would be a peaking coil to check....perhaps the contrast control is open ?

Do you have a scope?

jr

Nah, I've been really wishing I had a scope, though. Most of them I've seen are a bit expensive, other than a Tektronix? 555 I saw recently for $50. Didn't feel comfortable bidding on something I know nothing about.

I found that R31 ( 1k ) was out of tolerance awhile back and replaced it, but it didn't change anything. I think I recall that 220k tested okay, but I'll have to pull the chassis out again tonight and take another look. Not sure about the .1 capacitor, though. My multimeter can check capacitance but only once I've pulled it out of the circuit. The contrast control has been making the brightness go up and down as if the pot is working, but it's not "contrasting" anything. I'll be sure to look at those peaking coils, too.

I ran out last night to check and see if Home Depot had those adapters for the 300 ohm connections in the back of my tv. They didn't, so I waited and got one from Radio Shack today since the old one was messed up. But, to make the trip worth something while I was at Home Depot, I picked up some Howard's Restore-A-Finish in mahogany for my cabinet and a pack of fine steel wool. Today, the weather was nice so I immediately jumped at the chance to do something I've been wanting to do for a long time; fix up that scratched cabinet! It really didn't look too bad already, especially from the front where there were maybe only a dozen or so very small nicks that were somewhat noticable. The sides and top didn't fair so well. They still looked "okay" but were scratched beyond belief in some spots, especially the left side.

The Howard's stuff really did wonders for this type of damage without too much work at all. I think it took a couple hours with a bit of drying in between. I was pretty liberal with the top and sides, but very light with the front where I wanted to merely "touch up" the trouble spots. I still ended up rubbing a thin coat over the whole front end, although careful to avoid to the grille cloth.

http://img145.imageshack.us/img145/7222/img0431w.jpg

http://img813.imageshack.us/img813/2727/img0428f.jpg

http://img580.imageshack.us/img580/1872/img0433x.jpg

http://img137.imageshack.us/img137/5907/img0432l.jpg

The scratches are practically invisible and that color is just amazing! It's like I'm slowly turning the clock back 50 years. I could still touch up a few more spots and maybe wax it, but for now I'm happy with it. Now I'm just waiting on some rather expensive Krylon gold paint to get here so I can finish up the control panel. I've still got the chassis out so I'll be investigating the video output section tonight. More to come soon!

Looks nice! I'll have to try that stuff.

Concerning using a DVD player: Most VCRs will have a set of AV inputs (Yellow/White). You can hook your DVD player into this and just set the VCR to use the inputs.

A 6BA6 may also work in place of a 6AU6 if you have one to test with.

Oh yeah, I forgot to mention that I did figure that out recently! I had been playing cable channels and a DVD player by hooking it up to the VCR input jacks. The VCR actually makes it so that I don't really need a converter box, since I can flip through all of our cable channels on it. ( We only have basic cable, and this VCR goes up to like 200 channels or something ) No remote, though.

I already have a NOS Zenith 6AU6 on the way, but... I do have a GE 6BA6 on hand that came out of the same RCA radio chassis that I borrowed the audio output transformer from. I had set it aside as a possible replacement for my television because at some point, I swear I saw it in the tube lineup. Then, I checked back and didn't see a 6BA6 and dismissed the idea because I realized that I must have been thinking of the 6BE6 which is used in my set. I didn't know they were compatible.

Well, I swapped out that 6AU6 for the 6BA6 and it didn't seem to help. If anything, I think the buzz got worse. I tried making minor adjustments to the sound cut-off coil, no results. I tried the intercarrier coil, but it didn't feel like my allen wrench fit it. I know putting the tool down into the coil made it louder. I would have taken some voltage readings, but at one point I reached and turned the fringe lock and I heard two sharp cracks. That scared the crap out of me, but I checked and found no capacitors blown, no visible signs of arching. Maybe a shard of the steel wool I used earlier got into something? I did find that the way I had things positioned, the speaker wire was up against the low voltage rectifier tube and it got stuck to it and when I pulled it off, I realized it had melted slightly from the heat. That's the hottest corner of the chassis, so I made sure to reposition the speaker wire afterward.

I checked a bunch of resistors in the video output section but I swear I can't find anything amiss. I think I found one of those peaking coils, and it looks like something coated in wax with a red dot on it. It measures 8 ohms, compared to the 10 listed on the schematic.

Either way, the picture is still washed out when I adjust for the best sound output. I can make it contrast better by turning the AGC down, but then the buzz gets really loud. On one channel, I actually got the sound to work pretty good and the buzz was barely noticeable. Then a commercial came up and it was buzzing again.

Could the video signal coming in be to hot? I know some modulators are on the hot side. I notice this with my 53 zenith.

Could the video signal coming in be to hot? I know some modulators are on the hot side. I notice this with my 53 zenith.

Good point! I use something like this when connecting a DTV converter to older sets:

http://www.solidsignal.com/pview.asp?mc=03&p=1296F&d=20dB-Variable-Attenuator-for-VHF-UHF-HD-OffAir-Reception-1296F&c=Signal%20Variators&sku=853748001293

RS sells/sold them also but I have not see one in a RS for a while. Note that on the RS unit "min" means minimum attenuation, NOT minimum signal.


jr

did you ever try the comp signal at the video amp grid like I mentioned a while back?

Good point! I use something like this when connecting a DTV converter to older sets:

http://www.solidsignal.com/pview.asp?mc=03&p=1296F&d=20dB-Variable-Attenuator-for-VHF-UHF-HD-OffAir-Reception-1296F&c=Signal%20Variators&sku=853748001293

RS sells/sold them also but I have not see one in a RS for a while. Note that on the RS unit "min" means minimum attenuation, NOT minimum signal.


jr

I should get one of those. I kick myself for not grabbing some pads when I worked at the cable company.

Alrighty, I've got one of those Radio Shack variable attenuators on the way. Do you suppose there may be a chance that'll help with the washed out picture or with the buzz... maybe both?

did you ever try the comp signal at the video amp grid like I mentioned a while back?

Actually, I meant to ask you about that. I'm a total rookie with this sort of thing, so honestly I'm not sure what a "comp signal" even is.

on a DVD or converter box there is a jack that says 'video out" this is the composite video, it is the same as what comes out of the video detector (if the tuner and IF strip is aligned correctly). it is the video signal with the sync pulses but no audio.

the idea is to couple that video out directly to the grid of that video amp tube.

To be safe you should use a large value film cap, like a 1 uf. take the cap and put a alligator clip on one side of it, then connect the cap to a shielded lead center tap. to be extra safe, connect the shield to another cap again a 1uf and another clip, connect that to the metal chassis. the caps are there to protect against a hot chassis and a voltage difference at the grid (some grids will be biased to something other than 0 volts). The caps prevent damage to the convert box or DVD incase there is a DC potential, they will pass the video signal. there may be some losss of video signal (may look like smear) but should present a decent pic.

If so then you know the problem is in the tuner or IF. if still a bad pic then its prob in the video amp or after.

I dont recal if you checked the AGC voltage, you could also try clamping a variable DC power supply (or even a couple D cells and a pot to make up a varialbe DC power supply). too much AGC will kill contrast.

One thing, a long shot, but would not hurt to check is the detector diode, I did not look to see if you can check in circuit but I would try it.

I would try the video composite signal 1st, if you get good conrast then move on to the AGC, and check the video detector diode with a DMM in diode check mode.

Remember the diodes are VERY heat sensitive so the must be heat sinked when soldering. Often a diode is destroyed when working on a set and replacing a part that shares a term stirp lug with a diode. (germainium diodes anyway, modern diodes are silicon based and are very heat resistant).

one last warning, WHENEVER hooking up test equipment, like scopes, vtvm,signal gens, anything, I check for a voltage at the test point connections, in this case the chassis and the grid. if you ever hook up a scope to a hot chassis radio or tv you remember not to forget checking the next time....

I also one time hooked up a DVD video out with out the cap to isolate (it was zero volts so not really needed) to the grid of the video tube... did I say grid, well I mistakenly hooked up to the PLATE of the video tube. Smoked my DVD player...

the cap prob would have saved it (not sure about that since it would still have gotten a good pulse) but the real save would have been if I had just check the connector for voltage before pluggin it into the DVD.

do all your setups with everything off, check the plugs/jacks/probles for voltage BEFORE hooking up to the equipment after powering up the set you are working on. just use a DMM on them and check for both ac and dc.

Yeah, I have had success hooking up my DVD player in this manner. In fact, on sets I have restored for other people, I have added A/V jacks, as most folks don't even want to fuss around with a tuner anymore.

But I sure learned my lesson one time-I hooked up composite video directly to a hot chassis set-one of those awful GE split B+ sets. It very slowly fried the video output, creating an overloaded mess on the screen before I realized what was happening. It didn't totally ruin the DVD player, but the video out was trashed. Luckily, the luma out jack still works, which works just fine for fixing these old sets.

...The scratches are practically invisible and that color is just amazing! It's like I'm slowly turning the clock back 50 years. I could still touch up a few more spots and maybe wax it, but for now I'm happy with it....

Lookin' good :thmbsp:
I've used Howard's a few times before and really like it too. One downside though - it will fade after a while. They recommend Howard's Feed-d-Wax. It's orange oil and beeswax - great stuff :)

Yeah, I think I'll get some of that stuff to maintain the finish. I know they recommended using that on the back of the can rather than using some kind of lacquer or other finishes over it. I don't expect it to be really glossy, but I would like to keep it from becoming dull or hazy.

Well, I just got back from North Carolina today and got some things in the mail. I got my attenuator, a 12BY7, and a 6AU6. I've tested the set after installing both tubes and the attenuator but not adjustment seems to remedy any of my previous problems. The sound still distorts and buzzes pretty bad on most channels, and I have very little contrast. Back to the drawing board, I guess. I'll be pulling the chassis back out and going over the video and IF section again following some suggestions I've heard here and see what I can find.

UPDATE: By the way, that fringe lock control caused a sudden pop again last time I tried adjusting it. I'm not sure what it is. It sounded like something arched and there was a flash inside the set, but no burn smell and no change in performance. It has NEVER done it other than when I've turned the fringe lock to a certain spot. Pretty unnerving...

Well, I just got back from North Carolina today and got some things in the mail. I got my attenuator, a 12BY7, and a 6AU6. I've tested the set after installing both tubes and the attenuator but not adjustment seems to remedy any of my previous problems. The sound still distorts and buzzes pretty bad on most channels, and I have very little contrast. Back to the drawing board, I guess. I'll be pulling the chassis back out and going over the video and IF section again following some suggestions I've heard here and see what I can find.

UPDATE: By the way, that fringe lock control caused a sudden pop again last time I tried adjusting it. I'm not sure what it is. It sounded like something arched and there was a flash inside the set, but no burn smell and no change in performance. It has NEVER done it other than when I've turned the fringe lock to a certain spot. Pretty unnerving...

Did the attenuator have enough range to take the reception from "strong" down to a weak snowy picture?... and you still had buzz?

The pot problem could be related to dendritic growth... a growth of tin or lead "whiskers" from the pot body, which can short it out/contact the wiper as it moves. Humidity and electric field contribute to this crystal growth... might want to take the pot apart and check it/clean it. Since the pot can affect video and sync pulses, it might be part of the problem that you are having.
jr

This is the attenuator I was using:

http://cgi.ebay.com/Adjustable-TV-UHF-VHF-75-Ohm-Bidirectional-Attenuator-/350235582082?pt=LH_DefaultDomain_0&hash=item518baade82

It seems like the MIN side is mostly the same as what I have without it, and the MAX side gradually turned it to distortion and static. Referring back to your previous post about these, that sounds about right. So yes, the MAX attenuation results in a more snowy picture and finally nothing but static. The buzz was present when a picture was present, past that it's all noise.

I'll have a look at that pot when I pull the chassis out tonight. Honestly, I think it was the steel wool I used awhile back. A little shard of it must have rubbed off in there when I was doing some light polishing on a part of the chassis back there. Guess I won't be doing that anymore.

I have the same R-S attenuator and I never found much use for it.

I asked a question a while back, but I don't recall seeing an answer:

If you totally ignore the audio (turn it all the way down), is there a combination of picture controls -- brightness, contrast, etc. -- that gives you a nice picture?

If the answer is Yes, then perhaps you can focus on the audio.

Just looking for a simple way to isolate the real problem. Some times, trying to "fix everything at once" leads you down blind alleys.

Phil Nelson

Well, if I turn down the A.G.C delay about halfway and turn up the brightness, the picture has much better contrast. Now when it's set like that, turning the contrast up and down still doesn't improve it much. It's just as if the brightness and contrast control are performing the same adjustment. But yes, setting the A.G.C lower improves the picture quite a bit, granted it's still not as defined as what I see on some televisions of this vintage. I think I'll post a video on YouTube and link it here to demonstrate what it's doing:

http://www.youtube.com/watch?v=b2xBml-w8CI

The set now has NOS tubes in the IF section ( 3 6CB6's ), a new sound limiter tube ( 6AU6 ), and a video amp tube ( 12BY7), all of which were probably unnecessary but at least I know I don't have a weak tube. I haven't touched the sound discriminator ( 6BN6 ) which has a 2 x .01 ceramic cap in use that I might could replace. I have a couple .01 film caps that I bought just in case. It's just a hard spot to reach being that the tube socket is so close to the shaft of the channel selector. But, leadlike had told me that these caps can go open so that may very well be the case. One side of that does go to my buzz control.

Well, I pulled the chassis out tonight and decided I'd zero in on those ceramic capacitors I had mentioned before. I replaced that questionable 2 x .01 ceramic capacitor coming off my sound discriminator and found a .001 ceramic on my 6AU6 that had a bubble in it. I replaced the first with two .01 film caps and the .001 with another film cap and finally got everything back together.

The good news... is that this really made a difference. I think it's quite likely that the 2 x .01 was indeed open. I'm not sure about the .001 but I'd imagine it didn't hurt. While a few channels are still rather buzzy and distorted, the buzz is mostly eliminated or at least can be dialed down somewhere between the buzz control, fine tuning, and A.G.C delay. Channel 3 is still pretty hopeless, but I switched my RF converter to channel 4 and used that for my DVD input and I was able to watch Jack Benny without much disturbance at all. I have to turn the A.G.C. really low before the buzz becomes apparent and by then, the picture is breaking up.

I'll be sure to post a new video tomorrow on YouTube. With any luck, after making some adjustments and perhaps replacing a couple other small components, I might be able to wrap this project up!

The Krylon premium 18k gold plate paint I ordered came in today so I went ahead and cleaned up the control panel and gave it a few coats. Once it dried, I went in with a white paint pen and touched up the "Zenith" logo. I could have done a cleaner job and I wouldn't say the paint is anywhere near as glossy as I'd wished, but at least it's a proper shade of gold. I'd clear-coat it but honestly, I don't how that would work out over this paint. But overall, I'm pretty pleased with it.

http://img843.imageshack.us/img843/203/img0554zw.jpg

http://img821.imageshack.us/img821/2342/img0557t.jpg

After I replaced those ceramic capacitors, I've been able to turn the A.G.C. delay down without being ravaged with buzz nearly as badly as before. So, the contrast is much better now although it might could still do with some improvement. I'm not sure how these sets performed when new, so maybe they didn't contrast all that great for all I now. When I play DVD's now, the sound is quite good when playing the actual episodes. Only the menu screens cause a lot of buzz. I get the same effect on the cable channels. Some are pretty watchable, others are still distorted and buzzy. The one's that do sound okay, often buzz when the screen goes from bright to dark, etc.

Here's some things I still need to attend to:
Missing knobs ( fine tuning, tone control, contrast, etc. I've got 3, and I think I should have at least 4 more )
AC Line Cord ( non-polarized brown cheater cord would be fine )
Chassis Bolts ( It was never bolted down from day one. Yep... explains why the old CRT was trashed, huh? )

At least for the moment, it's a mostly functional vintage television! Sure is a lot more entertaining than a fish tank.

Many TVs of that vintage will buzz on a scene with great light/dark contrast, such as a menu screen or movie credits. If it sounds good otherwise, your audio may be close.

Your TV should be capable of good contrast. Here's a 1950 RCA tabletop:

http://antiqueradio.org/art/RCAT-100WrongTrousers01.jpg

That cabinet looks terrific.

Phil

The Dick Van Dyke show always looks better on a real B/W TV!

You are down to the finish line, now. It's really looking good!

Bruce

Good eye, Bruce! I had Dick Van Dyke playing on the DVD player. I have this set I bought at Wal-Mart with 65 hours of old tv shows. I think this episode was about an italian guy painting their living room.

Yeah, I'm not sure about the contrast. I think I've cancelled out the chance of any bad tubes, unless 1B3 tubes get weak and cause poor contrast somehow? I don't think that would happen, but it was mentioned in one of those repair books I've got. I have a picture of my contrast/video section. I had a hard time matching some of these weird components to the schematic:

http://img163.imageshack.us/img163/5019/img0391vt.jpg

Wow, my labeling didn't work out so good. Anyways, there's some capacitors listed that I couldn't find, as I recall. Those little cylinder/disk things around the sound take-off coil looked like tiny resistors or something, and I'm not sure about that green thing that's marked with paint dots like an old resistor. There's a similar one that's red like this and where I'm looking on the schematic, it mentions a capacitor. I wasn't sure if these were were caps, or resistors. The peaking coil, that someone had suggested might be open, appears to be that "blob." Looks like a resistor with a coil around it, coated in wax. Am I right? It said 10 ohm on the schematic and this measured 8 ohm on my multimeter.

I've been meaning to apply that video signal to see if the problem is before or after the video amp, but I don't seen to have any spare .1 capacitors to protect my DVD player.

ID peaking coil Correct!
Green cap with the yellow/purple/black dots = 47 uuf shown across sound takeoff xfmr ... 22k resistor just below the green cap.
Little disk circled is likely the 3.3 uuf cap on the sound takeoff xfmr.
jr

Wow, so those are capacitors... weird. Are these considered ceramic or wax, or what? I've never seen much information about these. Reliable? I know they're small values, but they are right there around the contrast control, namely that C32. It's hard to believe that such small caps could cause my contrast to work the way it is, but who knows. Also, my set doesn't have a screen register control on the front, so I'm guessing that R25 would be a fixed resistor in this case rather than a pot. I'm not sure if the screen register has much bearing on contrast, though.

Well, I have never had a problem with the small value ceramic caps, but anything is possible when we are dealing with 50 year old parts...
jr

I'm having a little trouble reading the schematic because of the resolution and I don't remember everything you've tried.

Have you checked the contrast control? It has four terminals instead of three so it's not as straightforward to check as a normal pot.

For it to affect the brightness the way it does it must be shifting the DC level at the cathode of the CRT. One side of the pot goes towards the plate of the video output tube which is at about 98V and the other towards the screen of the same tube which is at about 155V, if I've read it correctly. It looks like the cathode of the CRT is at about ~130V ? So, the DC level will shift some when you adjust it, but it should be over a limited range. around 130V. If the 4uF electrolytic tied to the screen, pin 8 of the video output tube, were leaky it could cause that level to be off which could cause a larger shift in the DC level at the cathode when you adjust the contrast.

Probably not much help, but just a thought.

John

Uh-oh... :para:

I was just running my set for about 10 minutes and while I was adjusting the bulls-eye tuning a bit, I started to notice this little "hiss" coming from inside my set. I hadn't ever heard that before. Awhile awhile, it started to get louder. I turn my brightest up and the sound get's a bit quieter, but if I turn it lower the sound get's louder. I'm almost certain it's coming from the high voltage cage. Smells like... static electricity.

As much as I hate to ask, can a failing flyback cause contrast problems?

ID peaking coil Correct!
Green cap with the yellow/purple/black dots = 47 uuf shown across sound takeoff xfmr .
Little disk circled is likely the 3.3 uuf cap on the sound takeoff xfmr.
jr

These are ceramic, and rarely go bad. You shouldn't need to touch them.

Well, that sound coming from the HV cage could be causing your problems. Maybe not a failing flyback, but rotting wires, etc could be discharging some of the HV before it gets to the picture tube. My CTC-9 had lousy HV until I listened in and heard a hiss like yours. I switched the lights off, and I could see the tube cap was glowing purple, like with a heavy static discharge. Looking closely at that cap, I saw it was cracked, and bleeding HV.

Of course, most of your HV stuff is UNDER the chassis, so you'll probably have to pull the whole mess out, and run the tv on its side on your workbench to get a visual on that hissing sound's source....

Yes, powering it up in total darkness may let you locate the Evil Spot quickly. That has worked more than once for me.

I would not run it for long periods in this condition. High voltage is escaping to a place where it's not supposed to be -- 'nuf said.

Phil Nelson

Alright, well as it gets dark tonight I'll be able to turn out the lights and monitor the chassis on it's side. The idea of a HV leak sounds pretty scary, but needless to say I won't be touching anything. I can tell you that a piece of wax had fallen off the underside of my flyback awhile back. Most of the wires were in okay shape from what I could see before, but I'll just have to see.

Well, that was creepy. But here's a photo I illustrated to show where it is. I could barely see it, even with the lights out:

http://img222.imageshack.us/img222/4016/hvarch.jpg

This is the bottom side of the flyback where that wax fell off and it seems to be running towards that bracket with the green wire you see there. That wire goes directly to the HV rectifier.

http://img259.imageshack.us/img259/764/img0563m.jpg

The white wire comes from the HV rectifier and goes to the anode of the CRT. The blue wire on the side of the flyback there goes to the top cap of the horizontal output tube.

Anyways, I couldn't tell if the voltage was leaking into the actual wire or just into the bracket.

Corona dope? No, I am not calling names :D...

General cement made/or makes a thick gooey black paint (in a small bottle with an applicator brush) that is painted over the problem areas. This may still be the "product of choice" for these problems... don't know... people might be using RTV or something else these days.

jr

Update: Looks like the stuff is still available... even listed on Amazon (with awful shipping charges):

http://www.amazon.com/GC-Electronics-10-4702-Corona-Bottle/dp/B000B62YO8

Likely it can be found cheaper elsewhere.

I believe Corona Dope is classified as a rather nasty substance so the shipping tends to be high.

I have used GC corona dope with great results, but on smaller areas than this flyback.

People talk about recoating entire flybacks with RTV. If you search the forums, those discussions should turn up.

I assume the arc is jumping to the bracket because that's the closest path to chassis ground. You want to seal up the fly where the spark originates, of course (i.e., not paint over the bracket).

Again, I would not power up the set at all, or only for a very brief period, before restoring the insulation. I would inspect that flyback very carefully before covering it up. Let's hope the arcing has not damaged the flyback.

Phil

Alrighty, well I think I can probably get some RTV around here somewhere. My only concern would be how to get to the flyback so I can work on it. It has a few wires connected to it that aren't easily removed from the chassis, such as the little plastic cap on top of the horizontal output tube. Should I actually desolder these from the flyback? I guess I'll see how much I can reach by just taking the screws out first.

I bought sensor safe rtv at the auto parts store. Worked great for my Zenith. Sensor safe is acid free.

Exactly! the stuff that smells like vinegar can eat copper wire/ circuit board runs.

http://newsgroups.derkeiler.com/Archive/Rec/rec.radio.shortwave/2006-03/msg01830.html

jr

Sensor safe RTV... sounds like a good idea. I don't think I need anything "eatting" my flyback. I was just at AutoZone awhile back with my dad. Maybe I'll check there and Advance and see what they have.

I was just thinking back on something that I thought I'd throw out there. It seems like when I installed my 4uF capacitor which filters the 12BY7 video amp, I seem to recall that I got the capacitor awfully hot. Seems like I had some trouble positioning it or something and the 100uF that filters the sound take-off coil is right next to that and shares a ground terminal. These capacitors were awfully little compared to many I put in. I wonder if I just got them too hot and damaged them.

I went out today and got some sensor safe blue RTV to coat my flyback. I coated the bottom half of my flyback where the wax came off, which effectively covered it a blue "icing."

http://img176.imageshack.us/img176/5174/img0567kj.jpg

After powering up the set and monitoring it, I've noticed now that that the "hiss" is gone, along with that troublesome blue arch. Still another trouble remains...

http://img221.imageshack.us/img221/7484/img0566b.jpg

I kept hearing a little "tic.. tic, tic..." coming from somewhere down here, and this time it doesn't seem to be arching from the flyback itself. I turned out the lights and could make out a faint little arch jumping from somewhere on this copper-colored thing to the cadmium-plating support bracket below it. I didn't hook up an input, but noticed that I couldn't seem to get any horizontal sync. I'm inclined to think that there's a bare spot in one of these wires going to or from the 1B3 that's leaking somewhere.

I see a fair amount of dust and such on that tan colored piece of plastic. That dust and dirt can create leakage paths for very high voltage. Cleaning it may get rid of that tic-tic-tic.

Isopropyl alcohol usually cleans up that soft soot pretty well. I'd clean everything you can reach. A soft artist brush is good for getting into tight spaces.

Phil

I took some time to clean up around this area with isopropyl alcohol, a small brush, and some cloth and I think I got rid of a ton of dust and black smut. I checked the wires, made sure they looked reasonably clean and cleaned up that plastic bracket and the area around the 1B3 tube.

Trouble came after I powered it up again. After about 10 seconds, I got some vicious arching from what looked like the bottom of the 1B3 tube socket. I didn't have to turn out the lights... it was just a sudden, wicked scorch of blue and orange. I didn't sit around and watch the show, obviously.

I took a close look at it and could only figure that maybe some of the alcohol got in there and didn't dry completely? I powered it up again, and saw no lights but heard a sizzle so I shut it off again and tried to blow it out. After the third time, the sizzle faded to barely nothing, but I can still hear a little hiss or two here and there from the bottom of the tube socket.

Gosh, if it's arching inside the bottom of that enclosed tube socket... I don't see any way in the world of getting to it.

Remove the tube and let it dry overnight.

UPDATE: Oookay, apparently she's fine now...? I went back in there to poke around after I posted this and the set powered up without any problems. I hear no hiss from the flyback, no sizzle from the 1B3. Just the nice soft hum of the transformer and a purring raster. Maybe I really was just a little too heavy-handed with the alcohol, after all.

Point taken, though. I'll make sure it has plenty of time to dry overnight and I guess I'll plug up my inputs tomorrow and see what kind of picture I'm getting. Sitting as it is, the horizontal won't hold steady no matter what I do. I hope it's just the lack of signal.

It's possible the leaking of the flyback threw off your horizontal frequency. Probably adjusting the H-lock coarse coil will throw you back into range.

I see a fair amount of dust and such on that tan colored piece of plastic. That dust and dirt can create leakage paths for very high voltage. Cleaning it may get rid of that tic-tic-tic.

Yes, I would certainly agree. I have an air compressor. But find that even though they cost too much, those cans of compressed air for computers and keyboards are excellent for a delicate job like this. And, careful application of liquid cleaners with Q-Tips gets the job done. Sounds like it takes forever but sooner than later, you sit back and it is done and nothing is ruined.

Without a doubt, that wasn't the easiest spot to clean up. I managed to get most of the dust and black smut out of there, though.

http://img132.imageshack.us/img132/71/img0574zn.jpg

I went ahead and coated a little more of the flyback up along the backside and towards the top of it. This flyback must have sat under layers of dust for years before I bought this set, and even though I had done a "cleaning" in that area before, I was very gentle about it. It didn't help any that this was all right in the path of the falling chunks of plastic from the yoke cover. Someone had suggested that I coat the flyback with something before, but I was caught up in chase of hunting down all the other problems that I never got around to it until now. I'm glad I did. Cleaning this up and coating the flyback seems to have really helped, and I'm not hearing or seeing any signs of a leak anywhere now.

After hooking up my coaxial cable, I was able to see that my horizontal was way off but after running the set for a few minutes and adjusting a few things, I got it to hold on most of the channels although it's back to losing sync when I change channels. It would stay that way for awhile at first, but now it's more of a 2 or 3 second delay.

I can't say that my contrast has improved, so I'm thinking I should try substituting that 4uF capacitor with another with the possibility that it may be leaking. As I said before, I think I might have gotten it too hot when I installed it.

Alright, now that my high voltage leak is patched up, I feel considerably better about taking live voltage readings on this set. I took a few earlier, but I noticed that the readings change noticeably depending on what channel the tv is set to, etc, so I looked in my schematics and it say's to take DC readings with no signal present, set to channel 2, and "normal" setting of controls. The last part of that I have a question about...

What would be considered "normal?" As in, should I set the brightness, contrast, AGC delay, etc, to their middle positions? Looking back at the schematics I posted before...

http://img840.imageshack.us/img840/9213/schematicsvideo.jpg

I'm wanting to check out this area and see what's going on with my contrast control. Maybe I'll have to take some measurements and adjust some of the controls and take note of what changes? I guess I just don't want to waste time giving you guys voltage readings that are off kilter due to something dumb I overlooked.

Huh, I just realized something. As of yesterday, I started this thread exactly 2 months ago. ( and I'm still not done :tears: ) Time flies, huh?

It's hissing... AGAIN. Sounds like another HV leak somewhere around the flyback. Why me?

What would be considered "normal?" As in, should I set the brightness, contrast, AGC delay, etc, to their middle positions?
Sounds sensible. If the manual has a separate procedure for setting the AGC, I'd follow that, of course.

Guess it's time for another peek with the lights out. Finding the HV leak may be frustrating, but there must be a solution. The TV worked when it left the factory, right?

Phil

Apparently I've had a couple leaks so far, the first from the flyback itself and then the next time I was getting something around the base of the HV rectifier tube. Well, that little "tic" inside the base I had went away completely and I've heard nothing sense until today when it starts hissing out of nowhere. I had the chassis back in the cabinet when it was hissing, so I pulled it back out to have a look and so far, I've had it running about 45 minutes or so with no sign of a leak at all. But... did find something; The metal base of the HV rectifier is charged with HV. I'm not sure if it should be or not, but it is. I can take a screwdriver with a ground wire attached to it and get a vicious arch just by putting the tip within about a quarter of a inch from the metal and the bolt that holds it on that tan plastic bracket. Now if it were normal to be charged like this, that would explain the plastic bracket... but anyways, I may just need to go back and coat the rest of the flyback and seal it up a little thicker, but that tube base sure makes me wonder.

... did find something; The metal base of the HV rectifier is charged with HV. I'm not sure if it should be or not, but it is. I can take a screwdriver with a ground wire attached to it and get a vicious arch just by putting the tip within about a quarter of a inch from the metal and the bolt that holds it on that tan plastic bracket. Now if it were normal to be charged like this, that would explain the plastic bracket...

They probably did that to act as an electrostatic shield to the wiring in the base of the HV rectifier. Otherwise the sharp ends of terminal lugs and wiring would cause corona discharge, which might make radio frequency interference. I suppose that there is normally a metal cage to keep it out of reach.

That's a good point, and it makes sense seeing that there's a small wire coming from inside the metal base that's soldered to the outside. There is a metal cage protecting this whole HV section, but of course it's on the topside of the chassis. I suppose that your Zenith serviceman would have known about the voltage present here, so I guess they saw no need to enclose it from the underside. I've tried to be careful around the HV section whenever I have the chassis running on it's side, but I did carelessly swing my probe past this area when I was taking some voltage readings and that's actually how I noticed the presence of HV in this area in the first place. A sudden zap from the base of the 1B3 caught me off guard, so I took note of that and later used the grounded screwdriver trick I use to discharge the CRT in order to confirm it.

I'm still going to be keeping an eye out for that HV leak, although it seems to be hiding from me at the moment. Perhaps another coat of RTV on the flyback will silence it for good. If this little nuisance will leave me be, I can get back to tracking down that contrast problem I've yet to cure as of yet.

I'm still going to be keeping an eye out for that HV leak, although it seems to be hiding from me at the moment. Perhaps another coat of RTV on the flyback will silence it for good.

Don't overlook putting the RTV on the sides of the HV winding. Many flybacks had a coating of thick wax or such on the outer half of the HV winding, made it look like a car tire.