Sigh.

If you remember, I got this set from ebay a couple of months ago. I've made some progress on it but still have a way to go.

The main problem seems to be tuning. At first, I was getting nothing at all on VHF. After cleaning the tuner some I started picking up channel 3 (it's attached to a DVD player), but only if the set is tuned to channel 2. I can pick up channel 4 if the set is on 3.

Off the air, none of the VHF channels work. I can get sound on a couple but no picture. Messing with it, I finally realized that the fine-tuning control does diddly (and I checked to make sure it was actually turning the little fine-tuning slugs; it is.)

For a while there, I had color on Channel 2/3, but the picture was slightly de-tuned. I can pick up color on UHF but only if the station is de-tuned enough to make it almost unwatchable.

Last night, I had no color on VHF at all. I also seem to have my choice of picture OR sound; I can get a great picture on channel 2 (DVD set to 3) but no or really bad sound. On channel 3 I get really good sound but no picture, no matter how much I fiddle with the tuning.

On the advice of others, I've replaced the three video IF tubes, the mixer/oscillator and RF amp in the tuner, the color oscillator, and the HV rectifier (that last to fix a size problem; it worked.)

One of the fellas at antiqueradios says it might be a problem with the AFC circuit. How can I find it, and what should I do with it when I get there? :dunno:

Can anyone thing of anything else I should try? Please remember that I only have the tools I've been able to fashion out of rocks and sticks...:D

Thanks in advance. I knew I should have taken a picture of it when the color was working...


veg

Can you find an AFC on-off switch? I don't know if it was ever common to have it permanently on. Usually, you were supposed to turn it off, adjust fine tuning, then turn it on to "lock in" the adjustment.

Well, color me embarrassed....

Yes, I really did verify that the fine tuning knob was twiddling the f-t slugs. I saw it with my own eyes every time I had the tuner out of the cabinet.

Can you tell where I'm going with this?

Yesterday it occurred to me that maybe, just maybe, when the tuner was mounted the slugs weren't turning. It was a long shot, but I figured it would be easy enough to experiment with.

So I pulled the channel/fine tuning/UHF numbers dials off the set and put back only the channel and fine tuning. The UHF dial was the last one in the "stack" so that's the one I removed.

Lo and behold, the fine-tuning actually worked! I now have a good picture, good sound and good color!

Woohoo!

Of course, the set still needs to be converged, but still. Oh, and the picture looks a lot better than the photo shows. I might have been a little shaky at the time; see below.

I guess to pay for my stupidity, I got majorly defibrillated last night. While doing the static convergence I managed to touch something I shouldn't have.... Yow! Practically knocked me on my a$$, and the smell of burning hair (or flesh) was potent.

But at least I've learned my lesson. Yes, I will remember this for next time.

Thanks to all who helped with this little project--couldn't have done it without you!

veg

Bit of an update. A sad one.

During the Super Bowl yesterday, the picture got really dark then disappeared altogether. Didn't smell anything burning, which I'll take as a good sign, but still...

veg

could be the HV regulator, rectifier, damper tube, HO tube if the high voltage is gone. Check video sections of you still have HV

could also be input filter caps if you haven't changed them

Just for the heck of it, I fired up the set last night and it worked just fine, so go fig. I did notice that the sound comes on well before the picture does and the picture itself seems to take longer than necessary to get going. Sort of like starting a car on a really cold morning.
Oh, I only had the set running for about 30 minutes.

veg

Loose connection, maybe one of the tube sockets?

Having the set die during the Super Bowl I can deal with. But last night it pooped out in the middle of Amazon Women on the Moon.
How DARE it?
Seems I can only get about an hour of time out of the set before the picture gets dark and fades away. I'm guessing that if I go try it out tonight it'll be just fine.
For a while, anyway.

veg

veg, Most likely a high voltage tube, BUT a video tube or the focus tube could do it as well. Have seen that on plenty of RCA's. Not sure of your sets design tho....

Well, I sent the HV regulator, damper tube, HO tube and shunt (??) tube off to "Dr. Roy" at Radio Tube Supply (http://www.radiotubesupply.com) for testing, so we'll see what's what.

If it turns out to be the flyback, how hard would it be to find, and how hard to replace? I don't have the part number with me--the SAMs is at home.

veg

This sounds like a thermal problem...not likely tube related as a weak tube will be weak all the time and will not gradually change over the course of an hour.
It sounds like the set is losing horizontal drive signal...some freeze spray applied around components in the horizontal oscillator area would probably be helpful in troubleshooting.
Also check for microcracks in the solder on the circuit board.

Since you have the SAMS it would be good to check all the voltages in the horizontal oscillator circuit and the output tube screen, grid and cathode voltages. (Don't measure the plate voltage with the lead connected as the HV will fry the meter.)

I took the set to an actual repair guy who said it needs a high-voltage transformer.

Is this the same as a flyback? Or is it something else entirely?

Don't have the part number handy, but is it something I could conceivably get (and install myself?)

Thanks!

veg

The HV transformer would be equivalent to the flyback. If you have the sams sometimes you can cross-reference the part number to a thoardson or another fly manufacturer. It can be installed yourself, but it usually requires marking and disconnecting lots of wires, and removing the HV cage.

That sounds a bit off... While not impossible, it's unlikely that the Flyback would fix itsself when cold. I bet the repair guy just didn't want to put the time into it, figuring you can't find a flyback. Also, it almost HAS to get super-blurry and also shrink from the sides or blow up large ("bloom") before fading out if the problem is loss if high voltage. If it isn't doing that, then you might have a video or CRT filament supply problem. Has anyone actually measured the high voltage after the picture fades out?

If the high voltage is "fading away" as it stays on for an hour, I bet something is changing value (cap or resistor.)

Just my opinion....

Charles

Yeah, there's no way the flyback could cause that. It's standard precedure for repair shops to quote an expensive, or impossible to find part when they don't want to work on something, or have no idea what's wrong with it. It sounds better to the customer than "we don't know what's wrong with it", or "you junk isn't worth our time".

Finding a flyback for that beast might not be real easy. I don't know, though. But I wouldn't start there.

I'm still leaning toward a bad connection. Like Charles, I think there needs to be some closer studies done when that picture fades out. Is is really losing HV, and if so, why? Even low HV will give something on the screen. I'd guess if the HV is still there with no raster than dig around the video circuit. If HV is being killed then fish around the Horiz osc.

Usually repair shops dont want to touch the old stuff , thats probably why he is telling you it needs a transformer . I aint no expert but with the little bit of tinkering i do at home old tvs , i would say its probably not a flyback if your getting a picture . But thats my opinion . My old magnavox had that issue and it was becuase of bad caps and a few bad resisters .