View Full Version : Weird issue with an RCA 730TV2
Kamakiri 11-03-2014, 10:25 AM Finishing up the restoration of a 730TV2, and I've got a weird issue with the vertical.....
It locks in fine. The height control is properly adjusted for the screen. Linearity is good. But, the image is about twice the size of what it should be.
I'm confused because I've never had this happen when there wasn't something wrong with the linearity or height......
Ideas? Someone mentioned that I might have an open in the linearity pot, but that seems to be fine.
Tom Albrecht 11-03-2014, 10:38 AM Your vertical oscillator is running at twice its proper frequency, so you're only getting half the image in each raster scan. That's why things are stretched vertically, and you see two overlapping images. Either the vertical hold control is not properly adjusted (most likely you would have figured that one out, of course, so that's probably not it), or something in the timing circuitry has gone bad. Check the resistors and capacitors right around the vertical oscillator. A short (leakage) in a vertical blocking transformer (if this set has one) could also cause this kind of problem.
Eric H 11-03-2014, 10:43 AM Check your caps in the vertical oscillator, I'm betting you have something like a .01 where a .001 should be or something of that nature. At least that's what happens to me.
Kamakiri 11-03-2014, 12:08 PM Possible. My 11 year old son did part of the recap. Think I'll have to double check his work and report back :)
Sandy G 11-03-2014, 12:30 PM Don't fuss at him, the boy's learning...If that's what it turns out to be... My dad would always yell at me over the slightest goof, which would make me even that much more nervous & uptight, & I'd INVARIABLY phck-up again... And then he wondered why I didn't like to do stuff w/him..
Kamakiri 11-03-2014, 12:40 PM Nah. Just the fact that he wants to learn this stuff is great. God knows I've made my share of mistakes :)
We installed the VOT in his Admiral 30A1 yesterday, and now there's no HV :sigh: . But that's what keeps this hobby interesting :)
vts1134 11-03-2014, 01:23 PM Someone mentioned that I might have an open in the linearity pot, but that seems to be fine.
Looking at your photo here I can say that wouldn't be from the linearity pot. I didn't know you also had a "double half" image in addition to your picture being vertically stretched.
Kamakiri 11-03-2014, 02:14 PM Yup. Checked all the cap values in the area, everything looks good. There's one mica cap in the area but that specs out dead on. Vertical pot is right on. But, the set DOES have a vertical blocking transformer.
I have a feeling that's it. It almost looks like there's black potting that came out from it at one point in its life. Just a little bit, but enough to make me suspicious. Gonna ohm that out next.
DaveWM 11-03-2014, 02:21 PM you should be able to hear it running slow. check resistors as well in the vert circuit.
Electronic M 11-03-2014, 03:33 PM Had that happen to me on the first set I restored...I was moving up north during the extended process. I could not read those stripe coded bumbelbee caps back then, and went by the sam's....BIG mistake! The parts list, and the schematic had the same cap rated a factor of 10 different depending on which you looked at. My set had a 'no video' issue that (in adition to making me walk away from the project for ~ 1 year) made what was likely a sam's typo induced error go undetected until I had lost track of the original caps to confirm... I did not have a good stock of caps when I got video back and was confronting the issue, and unsure of the sam's being the cause, I fixed it by playing with resistors in the vertical stage until it worked...
That was the first TV restoration I did, and that set made me WORK for it every step of the way. A challenge, knowledge building experience, and accomplishment if I ever had one in my high school years...
Kamakiri 11-03-2014, 07:08 PM Ohmed out the vertical blocking transformer. Should be 165 ohms primary, 1310 ohms secondary. Mine reads 211 ohms primary, 1645 ohms secondary. What do you think?
Tom Albrecht 11-03-2014, 08:40 PM I wouldn't really be able to draw any particular conclusion from these particular resistance readings. The thing that would cause a problem like what you're seeing would be if there is leakage between the primary and secondary windings, or from one of the windings to chassis. Try measuring that and see if you see any conductance, say, in the range of a few hundred K to 20 M ohms.
Kamakiri 11-04-2014, 10:04 AM About an hour before your post just for grins I searched out the part number and managed to find a NOS one on ebay with a 9.99 BIN. For that price since this one's out of spec anyway I decided to pull the trigger. Will update once it's installed.
Kamakiri 11-10-2014, 07:34 PM Well, got the replacement transformer in, and it ohmed out wildly out of spec, something like 50 ohms primary, 750 ohms secondary....so I didn't use it. I did, however, while I was in there, replace a few more out of tolerance resistors along with two other sections of the chassis mounted multi-value resistor (there were three, and only one tested bad....the one I just happened to have handy).
So, for the heck of it, powered the set up and this time only got retrace lines, and a very weak sync of some kind that I was able to lock in....no discernable video.
The weird thing is that when I was powering it up this time, I got what looked like an intermittent blue flashing short within the electron gun of the picture tube that came and went with the adjustment of the ion trap. Every time it shorted, I lost raster.
After the shorts stopped, I left it at a certain point where the picture was really bright and spent about 20 minutes fiddling with adjustments to try and get a picture back. No luck. During that 20 minutes though, the raster was nice and bright, sweep was fine, and the transformer ran cool.
Found a weak 12AX7 video amplifier tube, replaced that, powered the set up, and lost raster :(
My plan was to trace back the work I'd done on the chassis mounted resistor, but now I've lost raster, so I'm confused. Picture tube tests good still, and I tried a magnetic ion trap just for the heck of it to see if I'd get a picture. Nothing.
I do have good HV though. Hm. Kinda lost as to what might have happened.
Don Lindsly 11-10-2014, 09:52 PM Check for tin whiskers on the hold and size controls. Isolate the controls from the chassis and see if there is any improvement.
Penthode 11-12-2014, 07:44 AM Don't be concerned about the primary and secondary winding resistance. The failure mode of the transformer is leakage between primary and secondary.
Try taking in the replacement transformer.
Other than that, something is causing the oscillator to run fast. I do not think it is a resistor as they tend to drift upward in value. Capacitor leakage can. Check to ensure all the paper dielectric capacitors at oscillator grid including the integrator are replaced.
Kamakiri 11-22-2014, 11:25 AM The weird thing is that when I was powering it up this time, I got what looked like an intermittent blue flashing short within the electron gun of the picture tube that came and went with the adjustment of the ion trap. Every time it shorted, I lost raster.
After the shorts stopped, I left it at a certain point where the picture was really bright and spent about 20 minutes fiddling with adjustments to try and get a picture back. No luck. During that 20 minutes though, the raster was nice and bright, sweep was fine, and the transformer ran cool.
Found a weak 12AX7 video amplifier tube, replaced that, powered the set up, and lost raster :(
My plan was to trace back the work I'd done on the chassis mounted resistor, but now I've lost raster, so I'm confused. Picture tube tests good still, and I tried a magnetic ion trap just for the heck of it to see if I'd get a picture. Nothing.
I do have good HV though. Hm. Kinda lost as to what might have happened.
Fired up the Eico 944 flyback and yoke tester. Confirmed bad yoke. Welp, at least I know what to do next!
earlyfilm 11-22-2014, 01:59 PM Fired up the Eico 944 flyback and yoke tester. Confirmed bad yoke. Welp, at least I know what to do next!
Tim, just double checking before you sink some cash on a new yoke . . .
I'm assuming by "confirmed bad" you mean that the vertical windings check shorted.
I'm not familiar with the Eico tester, but other yoke and flyback testers will read "bad" if one forgets to open the resistor paralleling the winding. The 730 uses a 560 ohms across each vertical winding.
Kamakiri 11-22-2014, 05:14 PM I had thought of that. I wasn't certain if there was or not. I'll pull the yoke and confirm, thanks for clarifying :)
Username1 11-22-2014, 06:31 PM You have vertical deflection......... Full screen even..... I can't see it being the yoke....
.
Username1 11-22-2014, 06:35 PM Your vertical oscillator is running at twice its proper frequency, so you're only getting half the image in each raster scan. That's why things are stretched vertically, and you see two overlapping images. Either the vertical hold control is not properly adjusted (most likely you would have figured that one out, of course, so that's probably not it), or something in the timing circuitry has gone bad. Check the resistors and capacitors right around the vertical oscillator. A short (leakage) in a vertical blocking transformer (if this set has one) could also cause this kind of problem.
I'm placing my bet right here...... Tom is right, your problem is Vert Osc, and
the picture is too big vert. too....
.
Kamakiri 11-22-2014, 07:38 PM Right, but then I ran into this:
The weird thing is that when I was powering it up this time, I got what looked like an intermittent blue flashing short within the electron gun of the picture tube that came and went with the adjustment of the ion trap. Every time it shorted, I lost raster.
After the shorts stopped, I left it at a certain point where the picture was really bright and spent about 20 minutes fiddling with adjustments to try and get a picture back. No luck. During that 20 minutes though, the raster was nice and bright, sweep was fine, and the transformer ran cool.
Found a weak 12AX7 video amplifier tube, replaced that, powered the set up, and lost raster :(
My plan was to trace back the work I'd done on the chassis mounted resistor, but now I've lost raster, so I'm confused. Picture tube tests good still, and I tried a magnetic ion trap just for the heck of it to see if I'd get a picture. Nothing.
I do have good HV though. Hm. Kinda lost as to what might have happened.
Username1 11-23-2014, 07:05 AM Well, Ok, you have more than one problem... You need to do some troubleshooting.
First turn it on and hit it a few times..... figure out if it's got an intermitant.... Bad solder joints...
If you get a nice stable set while hitting it, then it's a part.... Look at what you don't have
and look in the part of the set that most likely lost it.... Raster no other stuff.... ??
Get out the block diagram and figure out where the problem might be..... Or at least
a place to start...
Hitting it... Use a wood dowel, 12" long, 1/2" dia. Bounce it off the chassis in different
spots. Gently hit the tubes, hit the coils, etc. You're just looking for a bad connection.
.
Kamakiri 11-23-2014, 02:15 PM Well, before I do anything, I'm gonna set the chassis on the bench and do some voltage checks to see exactly what is amiss. I'll have to be a little creative in suspending the picture tube, but it'll be pretty easy.
Kamakiri 11-29-2014, 09:37 AM Got the chassis on the bench. Found at least part of the problem. V1, the 6J6 RF amp, has only 88.2 VDC on pin 1 and 84.8 on pin 2. Should be 145 VDC on both.
V2, the 6J6 mixer, voltages are right where they should be.
V3, the 6J6 oscillator, pins 1 and 2 are high. Should be 75, I'm getting 98.
Problem has to be in those small white mmf caps that I didn't change. Are they anything special, composition wise?
Tom Albrecht 11-29-2014, 09:39 AM Those are ceramic caps that seldom fail. Generally OK to replace with mica caps.
Penthode 11-29-2014, 10:18 AM If the rf amp plate voltages are low, try adjusting the contrast (picture) control to minimum. There is no agc on this set and it may be the grid bias. I do not think the caps are bad and they are best left alone because of alignment.
Kamakiri 11-29-2014, 10:30 AM I was just working on an Admiral 30A1 and was thinking of THOSE caps. This set doesn't have ceramic caps. Oye. Working on too many sets at once....
Anyway, I discharged the HV and flipped the chassis over. Removed the screws on the lower tuner cover, and of course I can't see anything under the 6J6 because the tuner's in the way.
Still poking around in here.....
Kamakiri 11-29-2014, 10:44 AM Just to recap (har har), I have no raster on this set at this point but audio is fine, adequate HV (neon bulb test). Had a nice bright picture briefly, but doesn't now as outlined in the previous posts.
Usually at this point I'd start by measuring voltages working from the RF amplifier forward or going to the first video IF and working backward. Since I've got weird voltages right at the RF amp I'm kinda puzzled as to where to go from here.
Penthode 11-29-2014, 05:59 PM Just to recap (har har), I have no raster on this set at this point but audio is fine, adequate HV (neon bulb test). Had a nice bright picture briefly, but doesn't now as outlined in the previous posts.
Usually at this point I'd start by measuring voltages working from the RF amplifier forward or going to the first video IF and working backward. Since I've got weird voltages right at the RF amp I'm kinda puzzled as to where to go from here.
Did you set the contrast control to minimum and then check the RF amplifier plate voltage??!! Check the grid bias: I suspect the 6J6 is conducting heavily and pulling down the plate voltage. RCA did not include agc until the '48 models hence the contrast control feeds the rf and if grid bias.
Username1 11-29-2014, 06:25 PM Call the repair shop...... Is it still under warranty.....?
.
Kamakiri 02-24-2015, 06:33 PM Back on this one. Found a problem! The 3.3KOhm 1 watt resistor off pin 1 of the 12AU7 video amp that I replaced overheated and was open! Heady in my discovery, I soldered a 2 watt in place, and put the set back together.
Powered it up, and the horizontal output tube lit up like a Christmas tree. And then the smoke started coming from underneath the HV cage. Powered it down as quick as I could.
Dammit :tears:
jr_tech 02-24-2015, 11:27 PM Powered it up, and the horizontal output tube lit up like a Christmas tree.
Bright red plate, bright purple/blue ion glow or sparks and fireworks flying around inside?
jr
Electronic M 02-25-2015, 12:40 AM Bright red plate, bright purple/blue ion glow or sparks and fireworks flying around inside?
jr
Neon letters that spell the word 'BANG!' ? :D
Kamakiri 02-25-2015, 05:33 AM Bright purple/blue ion glow AND sparks and fireworks flying around inside. Wasn't too confidence inspiring. I don't get it.
Time to pull the chassis and see if I can see what went wrong here, but damned if I know offhand what it could be.
Kamakiri 02-25-2015, 07:03 AM Just pulled the chassis, and the damage doesn't look too severe. Appears that a couple resistors on the chassis smoked, as shown on the circled schematic below.
Not really sure where to go from here, hopefully someone has a suggestion....
kvflyer 02-25-2015, 07:08 AM You might want to check wiring. Could a part have been connected to the wrong terminal? Blue light dancing around inside of a tube is sometimes indicative of a short circuit down stream.
I remember in an earlier life, I plugged in a Knight-Kit amplifier. The 6CA4 had quite a light show inside of it. Yes, it was a shorted filter. Never made that mistake again.
"Just sayn'"
Kamakiri 02-25-2015, 07:11 AM Oh believe me, I'm not above making a wiring mistake. What KILLS me is that I had the sucker working and was trying to work through a vertical issue when I encountered this chain reaction failure last night.
I didn't change anything under the chassis since then, and nothing that I can see got bumped into anything else.
N2IXK 02-25-2015, 07:11 AM My usual power-up procedure leaves the horizontal output tube out until I verify the following:
Negative grid bias
Grid drive waveform
Screen voltage
DC plate voltage
Making sure that all of these look reasonable without the tube installed greatly reduces the chance of fireworks when the tube goes in.
Kamakiri 02-25-2015, 07:14 AM Right, but I didn't have any reason to suspect any other problem. This is what I was trying to fix when the raster dropped out. Found an open resistor on the 12AU7 and thought I nailed it.
http://www.videokarma.org/attachment.php?attachmentid=184761&d=1415031943
dtvmcdonald 02-25-2015, 07:21 AM I suspect you got bit by a random failure of some part, or a tiny
piece of solder from a recap lodged somewhere it wasn't supposed to be.
I had one of those each happen with my CT-100. No fireworks, however,
just no picture.
jr_tech 02-25-2015, 12:58 PM Wouldn't be the first time that a NOS or well used tube has suddenly cracked/gone gassy or shorted on turn on, especially if it has been subjected to a few bumps 'n thumps such as turning the chassis over for repairs. That's my hunch anyways.
jt
Kamakiri 02-25-2015, 01:03 PM I did check the tube. Although nearly flatlined after that meltdown, the tube wasn't shorted.
Anyone wanna fix this for me? I'll ship you the chassis and pay dearly :D
jr_tech 02-25-2015, 01:39 PM There is a possibility that the sparks/fireworks sparks flying around in the tube were the remains of whatever shorted (grid wire perhaps) and the short was cleared at the expense of 2 smoked resistors and a dead tube. I guess that I would replace the resistors and tube (and at least check the cap between the two resistors) and try again. carefully!
jr
Kamakiri 02-25-2015, 02:43 PM I can do that. At least I'll know what to half-expect ;)
Naturally I'll run through the tubes, and any component connected directly to the 6BG6. Anything else I should test or look for before another attempt? Aside from wires touching :eek:
Zenith26kc20 02-25-2015, 04:08 PM From the failed parts it looks like no drive to the horizontal output causing extreme saturation of the tube. It's overload roasted the resistors. Can you scope the control grid on the HOT with the cap off temporarily to see if the drive pulses are present?
Kamakiri 02-25-2015, 07:20 PM I just invested in a scope about six weeks ago, an RCA WO-33A. However, as of yet I don't have a clue how to use it, so no.
Learning how to use the scope is on my to-do list.......
jr_tech 02-26-2015, 01:15 PM I just invested in a scope about six weeks ago, an RCA WO-33A. However, as of yet I don't have a clue how to use it, so no.
Learning how to use the scope is on my to-do list.......
Those are cute little scopes... I keep a 3 inch Heathkit OL-1 as a nostalgia piece, such scopes would be fine for detecting the 15 kHz signal at the grid of the horizontal output tube. Does it work? Can you get a green line? Any response if you touch your finger to the vertical input? (like a 60 Hz sine wave) Those scopes are easy to operate, perhaps we can talk you through it?
jr
Phil Nelson 02-26-2015, 01:38 PM RCA WO-33A. However, as of yet I don't have a clue how to use it
You can download the manual here:
http://bama.edebris.com/manuals/rca/wo33a/
Not the greatest scan, but you can read the basics.
I have a WO-33A, unrestored and missing the probes.
http://antiqueradio.org/art/temp/RCA_WO-33A_Unrestored.jpg
My everyday scope is a much newer item. I haven't attempted to use this one for practical work; no doubt it would benefit from some service.
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
Kamakiri 02-26-2015, 02:25 PM Those are cute little scopes... I keep a 3 inch Heathkit OL-1 as a nostalgia piece, such scopes would be fine for detecting the 15 kHz signal at the grid of the horizontal output tube. Does it work? Can you get a green line? Any response if you touch your finger to the vertical input? (like a 60 Hz sine wave) Those scopes are easy to operate, perhaps we can talk you through it?
jr
I'd love you! :D
I actually have the RCA factory manual for it as well. Seems to work just fine, from a cursory plug in and adjustment.
jr_tech 02-26-2015, 04:09 PM I actually have the RCA factory manual for it as well. Seems to work just fine, from a cursory plug in and adjustment.
So it would seem that you are at least to "first base" here, and can get a trace of reasonable brightness and focus positioned on the screen... let me ask "what controls are you unfamiliar with?"
Do you have the matching probe?
jr
Electronic M 02-26-2015, 04:51 PM Yeah, the average tube era scope is not harder to set up than a monochrome TV that has had all it's user controls cranked to random positions by someone lacking knowledge/courtesy...
Zenith26kc20 02-27-2015, 09:28 AM The good thing about that little RCA is if you accidentally get across raw RF (damper or some other high voltage pulse) you won't have to start digging thru the vertical input amplifiers for fried protection diodes or worse!
Kamakiri 02-28-2015, 12:52 AM So it would seem that you are at least to "first base" here, and can get a trace of reasonable brightness and focus positioned on the screen... let me ask "what controls are you unfamiliar with?"
Do you have the matching probe?
jr
Basically, I'm not familiar with using it in any application nor do I know what I'm looking at when I see it. I have universal probes here, basically just wires with probe ends. Nothing else.
dtvmcdonald 02-28-2015, 06:49 AM Come to the ETF convention and have somebody show you how to use one.
They could have a workshop.
A calibrated scope is THE #1 tool for TV service. Second is a resistance-capacitance meter. Voltmeters (preferably analog) are third, since many charts list DC only and
its not always easy to figure out the DC average from a calibrated
scope trace.
A multimeter will, however, be used much more than an UNcalibrated
scope, which will still solve TV problems quite well.
Kamakiri 03-22-2015, 08:20 AM Okay, we're back on this set. Some interesting developments....
I replaced the 82 ohm resistor that burned with the same 1 watt, figuring that if it was going to burn up, I'd rather have that resistor burn up than have the resistor hold and damage something else. Everything else under the chassis spec'd out fine.
Now while I was under there, I looked at the Synchro-Guide pot and noticed, whoa, the slug's turned in so far that it's not sticking out the side!! I proceeded to turn the slug out so that it would. But wait a sec, there was nothing wrong with the horizontal!!! Damn!! I shouldn't have touched it!!
THEN I noticed that somehow I forgot to do a filter cap. What?? It's the one with two weird values, 250 uF@ 10V and 1000 uF @ 6V. Centering control bypass caps. Well, the picture did center out, so I'll order those on my next order.
I backed it out to where I thought it was, and then I noticed that the nuts holding it in place were loose. Well hm, I wonder if that's not the original one.
I proceed to put the set back together with a new horizontal output tube, and though I can't explain it, it came back to life! But now, I've got inadequate width, and the width control seems to do nothing. That aside, I've got a very predictable multiple image situation because like an idiot I screwed with the synchro guide control from the underside.
I have a feeling that I'm going to have to just use a plastic handled screwdriver with the chassis sitting on its side and the picture tube held in a jig of some kind in order to get the synchro-guide control to come back into range and have just a single image. Or, can I set it withing a range by resistance?
Another instance where using a scope would be handy, but let's disregard this for the moment as I have to get my hands on a proper probe.
The width, that I'm not sure about. I think that the yoke might have slipped back on the chassis because I had to adjust it back forward in order for the picture tube to hold in the cabinet. Maybe that has something to do with it as well?
But at least I'm back to something I can work with.....
timmy 03-22-2015, 02:30 PM now thats horizontal, it happened to me but the horiz hold pot was turned to much one way so backed it up it was good. but the width, i got that now swing the horiz hold all the way one way then back it up and see it it fixes itself. maybe the pot, they burn too. the hold and or the horiz size.
Electronic M 03-22-2015, 07:16 PM Does the manual for your scope show a schematic representation of the probe, and it's contents? If so you could probably make a half decent probe out of what is in your junk box. You don't need an exact probe and exact waveform amplitude to adjust the synchroguide. All you need to adjust it is an image of the wave shape with relative amplitude (one peak of the wave form to another) so you can get the point and the hump adjusted to the same height.
dtvmcdonald 03-22-2015, 09:06 PM The manual describes two probes.
One is just 3-4 feet of RG59 (or 6 or even 174) with clip leads
for ground and center conductor.
The other is a 10x probe. This has a 9 meg resistor in parallel with
and 8 or 10 pF ceramic or mica cap between the cable center
conductor and the clip. The cap is critical if and only
if you need reasonably flat frequency response, which that
scope may not be capable of.
To check scope frequency response, look at the waveform
on the video out of a DVD player playing a frequency
burst or sweep pattern.
Kamakiri 04-08-2015, 08:11 AM So here's where I'm at now.....
Have inadequate width, and horizontal foldover. I have the chassis out on my bench flipped on its side, and the picture tube held in a makeshift test jig. Width control does squat.
This pic is about the best I can get it just by turning the synchro-lock and horizontal hold. Getting the feeling that what I was doing with the synchro-lock in an earlier post wasn't the problem....I think I might have taken something else out with that spark show.
Now what HAS changed is that I now have a Tektronix T922 dual trace scope at hand with probes, so I can scope the waveforms if needed. Problem is that I don't know how :D . This is a really good opportunity for me to learn, as I have the set ready to test, and the equipment to do it. If I need to.
So, that said, advice as to where I go from here? :)
Kamakiri 04-08-2015, 12:12 PM Okay, well, y'know.....if you looked at my last post and said "look at the schematic, stupid....the answer's right there!!!"....well, you'd have been right.
I was wrong in assuming that it was one component that failed that I didn't catch. I decided to start just by looking at all the resistors in the affected systems, and go from there, thinking that the meltdown just overloaded a bunch of stuff. Tested the resistor to the width coil, found that it had doubled in value, and what do you know, I got some width back. Not all of it, but some.
I'm just going to have to go through each resistor in the affected systems, and test and replace them one at a time. Patience and persistence will win this battle.....
Interesting though that I have multiple horizontal images at this point. At least the vertical locks in solid. Now I have the exact opposite issue from when I started this thread.
Username1 04-08-2015, 01:05 PM You have no mystery, With several images on the screen you have a horiz osc.
running too fast.... = Capacitor in timing circuit too small....
Charging and discharging too fast, this often makes the peaks smaller, and a higher
possibly 2X frequency means the next stage is being fed something it's not tuned
for... So it's response is, and should be lower... = narrow picture....
.
Kamakiri 04-08-2015, 01:13 PM Since I didn't change any of the caps in that section from the very first picture in the thread where the horizontal was fine, it's possible that one of them got damaged or taken out in the "event".
Findm-Keepm 04-08-2015, 01:35 PM Here's some gemane info from RE - I've encountered similar problems with the synchroguide oscillator before, but always lucked out with simple fixes, either the tube or a ceramic cap drifting.
Off frequency could also be caused by a broken slug (core). Is the S-G core good?
Username1 04-08-2015, 01:58 PM L-C or R-C it can be the other part of the timing circuit, not the cap....
I don't remember "the Event" just some free time, looking at the pic.
.
Kamakiri 04-08-2015, 02:48 PM Basically the 6BG6 went up in a shower of sparks with sparks underneath. True cause is still unknown.
Kamakiri 04-08-2015, 02:50 PM Here's some gemane info from RE - I've encountered similar problems with the synchroguide oscillator before, but always lucked out with simple fixes, either the tube or a ceramic cap drifting.
Off frequency could also be caused by a broken slug (core). Is the S-G core good?
I'd imagine so, it turns freely and was good when this whole fiasco started. I've also checked the micas on the S-G (albeit with a Chinese hand held tester), and all caps off the 6SN7 and 6BG6. Everything there is good, including the tubes.
I read the articles, and it seems that perhaps I could do the adjustment with a scope. I do have one handy now, just need some guidance on doing it :)
Notimetolooz 04-08-2015, 10:58 PM As far as getting familiar with using the oscilloscope, do you have a square wave and/or sine wave generator? Some scopes like the Tektronix have a built in square wave source available on the front. It helps if you start out with a known signal source. By varying the frequency and amplitude on a generator you can see the effects on the 'scope. The fixed source on a scope like a Tektronix is used to check the adjustment of the trimmer on a 10X probe. That trimmer adjusts the high frequency response flatness.
Kamakiri 04-09-2015, 07:30 AM At this point I have checked everything in the entire horizontal section. Every cap, every resistor. Found a couple resistors that were 150-200% out of tolerance but still no appreciable difference in the picture.
It's time to try replacing the Synchro Guide can. Fortunately, I know where I can source a 630 chassis to get the necessary part.
Notimetolooz 04-10-2015, 12:23 PM I've been back tracking your story on this TV. Wish I had come across it earlier. Lot of twists and turns! It occurs to me that the reason the width control doesn't have much effect is that the horizontal frequency is off so much. The reactance at that frequency isn't correct. So I would get the frequency right first then see to the width problem. Which resistor was it that was connected to the width coil?
ChrisW6ATV 04-14-2015, 02:06 PM This is an excellent time to practice with your new oscilloscope. There are books on using them, including one or more I found online (Oscilloscope Fundamentals from Tektronix is one). It should not be hard to connect it to see the signal in your horizontal oscillator, then check its frequency by matching the number of pulses on the scope screen to the scope's horizontal sweep setting (such as 100 microseconds (or 0.1 milliseconds) per division, the squares on the screen each being a "division").
If I have it right, a 15.75 kHz pulse is 63 microseconds, so you should see about three of them per every two divisions on a scope set for 100 uS/div or 0.1 mS/div, and adjusting the horizontal frequency would change the width of the pulses on the screen (and therefore, the number of pulses per division). This is just one example of a scope setup.
Kamakiri 04-14-2015, 02:50 PM You're 100% right, and Notimetolooz, I'm sorry that I didn't respond to your question, honestly I just noticed it :)
I'll pick up on the 730 after ETF....for now it's buttoned up and has a nice coat of Pledge on it :) . When I get back on it, this thread shall continue :D
Electronic M 04-14-2015, 03:14 PM You don't want to use pledge on any furniture you want future generations to be capable of refinishing. It contains silicon which sinks into the wood and creates fish eyes in any new lacquer finish applied even after a strip and sand. The only finish that is immune is poly, and that stuff is sort of permanent once applied (which is why many restorers refuse to use poly).
Kamakiri 04-14-2015, 04:49 PM Well it really doesn't *need* refinishing. The flash of course brings out every last imperfection and now that I've taken the pic I'm gonna go grab the Howard's and do a little touch up. Man, look at the dust on the moldings, I'm slipping!! :eek: ;)
I have a thick piece of glass on top which protects the top from anything I happen to plop there :)
Electronic M 04-14-2015, 05:05 PM I stopped using pledge when I heard of the silicon issue because I don't want future owners of my stuff to not be able to refinish it properly. If you switch to old fashioned furniture wax or citrus oil furniture cleaner you get the same type of clean/shine without annoying any future wood workers that have to deal with the set for the remainder of it's existence.
Notimetolooz 04-14-2015, 05:48 PM You're 100% right, and Notimetolooz, I'm sorry that I didn't respond to your question, honestly I just noticed it :)
I'll pick up on the 730 after ETF....for now it's buttoned up and has a nice coat of Pledge on it :) . When I get back on it, this thread shall continue :D
Yeah, I figured you must have gotten busy on other things. I was getting into it, even downloaded the Sams from the Early TV Museum website. I noticed there isn't any waveforms on that Sams. See you at the conference.
I expect to be there all day Saturday then Sunday morning. I'm staying with relatives in Ohio. My first time there! :thmbsp:
Another Tim
Kamakiri 08-05-2016, 10:37 AM Remember this set? Yep, I still have it. Here's where it's at currently.
Replaced the Synchro-Lock, and it was working for about 10 minutes. All of a sudden, the picture shut off and the 6BG6 started hotplating. This was last winter.
Since I've replaced all of the obvious stuff, and gone far and above beyond that, this week I decided to stick in a new fly to see if that would cure the issue, since I had one here (was suggested by someone that I try that). Nothing.
After over two years, my disgust level with this set is high. I don't know what voltages are currently on anything because of that. If I can't fix this thing soon, it will go on Craigslist to be made into a dog bed and I really won't care :)
That said, please give me some advice on this thing. I'm at my wit's end.
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