Zenith 19L25 Chassis Restoration - Advice?

[RitchieMars]

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.



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:





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!



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.



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.

[bandersen]

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.

[RitchieMars]

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.

[jeyurkon]

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

Good work.

John

[leadlike]

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....

[RitchieMars]

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...?

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





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:



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.

[leadlike]

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.

[RitchieMars]

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:



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?

[jeyurkon]

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

[RitchieMars]

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.

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.

[wa2ise]

Originally Posted by RitchieMars

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.

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.

[RitchieMars]

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.

[wa2ise]

Originally Posted by RitchieMars

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.

[RitchieMars]

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!



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...



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.

[leadlike]

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?