Hi all. Good to be back. Life got really, really "lifeie". Re-configured the shop as well. Just got overwhelmed with TVs, parts and junk.

I'm working on the granddaddy of post war RCA TVs. The horizontal is completely unstable, "twitching" almost like something is intermittently arcing although I can't hear or see anything. It won't lock. C168 on the phase can, value 153, has been replaced in fact, EVERYTHING in the horizontal circuit has been replaced. I guess the first thing I should do is check for cold joints. All the tubes in the horizontal circuit have been replaced multiple times with known good tubes. Any suggestions as to where I should start?

BTW, just for anyone who remembers my issue with the T-65, KCS47 and the bent hourglass sides, it was the yoke swap I did. The original yokes are back in place and it's got a rectangular picture. Not magnetized.

The synchrolock circuit is a very fussy beast to tame! :(
When it works, it works very well, but when it misbehaves, It's a real bitch! :/

Yeah I can't even get a solid sawtooth for the horizontal frequency. I can get it to 15.75 KHz then it jumps all over the place and the trace goes haywire then it holds for half a second etc. Like I said, it strikes me that it might be an intermittent connection although all the coils ohm out so I think cold solder joints is where I should start.

No experience with the synchrolock circuit, so can only make ignorant comments:

1) I'd look for cold solder joints too, but not expect to find any if I had replaced all the parts

2a) Any possibility of having a replaced part value with the decimal point in the wrong place?

2b) Does anyone know of parts value mistakes in schematics depending on the source?

Edit: 3) is there a way to break the loop (like grounding the phase detector output) to see if the oscillator is stable or jumps around by itself?

There's an EXACT adjustment for the adjustment for the horz osc, in the SAMS, was that followed?

I have a similar issue with a 630 TS horizontal sync pulse getting lost before going to the oscillator.
Been sitting for months waiting for a fix after complete recap.
I'm working on it for another VK member who has a Philco 65 roundie for me as compensation.

First step is to check your work, one cap off by factor of 10 or to wrong spot can cause mayhem and we all have done it. :boring:

Synchro-guide is explained in RCA literature (can supply some if needed) and re-reading it may help both of us.

I'm enlightened by Wayne's last comment above; grounding a feedback loop can give a clue if oscillator itself has good output waveshape, part of adjustment procedure noted. (have a scope?) This may help uncover source of unstable operation.

There's an EXACT adjustment for the adjustment for the horz osc, in the SAMS, was that followed?

Yes I followed that procedure. The issue is the jumping and not the frequency. As far as any of the instructions saying "pull in the picture untill..." that's not possible. The trace is a 15.75 khz sawtooth for a half second and then nonsense then back to a sawtooth then....

I wish there was a way to post video on VK. It would clearly demonstrate the fault.

I have a similar issue with a 630 TS horizontal sync pulse getting lost before going to the oscillator.
Been sitting for months waiting for a fix after complete recap.
I'm working on it for another VK member who has a Philco 65 roundie for me as compensation.

First step is to check your work, one cap off by factor of 10 or to wrong spot can cause mayhem and we all have done it. :boring:

Synchro-guide is explained in RCA literature (can supply some if needed) and re-reading it may help both of us.

I'm enlightened by Wayne's last comment above; grounding a feedback loop can give a clue if oscillator itself has good output waveshape, part of adjustment procedure noted. (have a scope?) This may help uncover source of unstable operation.

I have checked my work but in a comprehensive solder check, I can confirm the values once again. I have the RCA service guide for this TV but I don't think it describes the Synchro-guide operation. It would be awesome if you shared it!

I have 4 scopes so I think we will be OK! I've tried 4 different oscillator tubes in this including ones that work in other TVs.

The socket for the sync discriminator (V123), the 6AL5 needed to be replaced. I've checked the work multiple times but I'll do it again.

Here is the circuit. Could the 6AC7 and associated components possibly be the problem? Ive switched it out with 2 different tubes and I pretty sure the pins are tight in the socket.

https://imagizer.imageshack.com/v2/1024x768q70/923/obK9WZ.jpg

The schematic says the grid of the 6AC7(pin 4) is -2 volts.
I don't think it would hurt to temporarily ground it, so I'd try the following:
1) put a scope or meter on pin 4 and see if it jumps around when the bad waveform occurs
2) if it is jumping with things normally connected, it could be caused by anything from the discriminator to the oscillator because they are all in the loop. I suspect you will see it jumping around.
3) ground pin 4 so the control voltage is constant = zero. Hopefully this only throws the frequency off some.
If the oscillator is now stable, you have isolated the problem to the discriminator. If the oscillator is not stable, the problem is in the control tube or oscillator.

Another thought - with set off, pull the Horisontal Oscillator (6K6-GT) and measure the resistance from pin 5 (R196/C172), looking for intermittent while adjusting Horizontal hold.

The schematic says the grid of the 6AC7(pin 4) is -2 volts.
I don't think it would hurt to temporarily ground it, so I'd try the following:
1) put a scope or meter on pin 4 and see if it jumps around when the bad waveform occurs
2) if it is jumping with things normally connected, it could be caused by anything from the discriminator to the oscillator because they are all in the loop. I suspect you will see it jumping around.
3) ground pin 4 so the control voltage is constant = zero. Hopefully this only throws the frequency off some.
If the oscillator is now stable, you have isolated the problem to the discriminator. If the oscillator is not stable, the problem is in the control tube or oscillator.

Another thought - with set off, pull the Horisontal Oscillator (6K6-GT) and measure the resistance from pin 5 (R196/C172), looking for intermittent while adjusting Horizontal hold.

All great ideas. I’ll try them tomorrow and post when I’m finished. Thank you!

From what I remember, these sets hate dirty video, if after following old_tv_nut's steps does not find any faults, one thing you may want to try is to feed in composite video, which can be done by removing the 4th pix if (v113) and feeding in video ( capacitor coupled) to the grid of the 1st video amp, pin 1, v115, and see if the h-lock is more stable.

From what I remember, these sets hate dirty video, if after following old_tv_nut's steps does not find any faults, one thing you may want to try is to feed in composite video, which can be done by removing the 4th pix if (v113) and feeding in video ( capacitor coupled) to the grid of the 1st video amp, pin 1, v115, and see if the h-lock is more stable.

Looks like I'm going to have a busy night when I get home!!!

OK an update. Twitch is gone. Reflowed all of the solder joints and I must have had a cold joint or joints somewhere. Horizontal frequency is good. The problem remaining is lack of horizontal lock. Vertical is rock solid but the best I can do with the horizontal is a very tenuous steady picture that starts to roll after about 4-5 seconds. Even when it's stable, it's not really stable. I can see it moving just a bit before it loses it. I don't know if this means anything but any sort of movement of the focus (not worried about focus...using the electrostatic 5" test tube) or contrast and brightness throws the horizontal off. The horizontal hold is more or less in the middle but once it loses lock it's very bad. I still couldn't attempt anything like the horizontal adjustments in the service data as they require a semi-stable picture. So it has to be an issue in this Synchro-lock circuit I guess. Any ideas other than some of the ones mentioned before? Should I check voltages on these horizontal circuit tubes???

The Rider service info has an explanation of the horizontal circuits with a couple of drawings of the waveforms in the sync discriminator. You might try looking for them.

The RCA docs are here.
http://www.antiqueradio.org/art/RCA630TSService.pdf

What it sort of sounds like, that the -100v source it changing drastically when you make those adjustments, and it's messing with the Horz sync, have you checked that it is stable when you adjust focus, contrast and brightness?
OR the other bias voltages when you adjust them?

Yeah looks like I have some more work to do with the multimeter and scope. Oh well, I solved one problem…I’ve got a picture stable in the vertical. I’m gonna run this down whatever it takes!

Just a shot in the dark, and a long one at that -- does the jug have a dag coating, and if so, could the dag have a flaky ground, or a floating dag "island"? I've seen a few weird effects that first appear sync-related but traced back to flaky dag.

Just a shot in the dark, and a long one at that -- does the jug have a dag coating, and if so, could the dag have a flaky ground, or a floating dag "island"? I've seen a few weird effects that first appear sync-related but traced back to flaky dag.

I think he said he's using a 5AXP4 for testing, I used a 8YP4 when I worked on mine, It had no Dag, and it did not cause any issues.

Yes it’s a 5AXP4. It doesn’t have a dag coating and I don’t think it ever did. Ive used it successfully in lots of early black and white 📺s

Sounds like this tv is one of those spooky mysterious flaky TVs where resonances and rogue RF signals wreak havoc on performance. I’ve always have had trouble with these “Ghost in the Machine” sets.

Sounds like this tv is one of those spooky mysterious flaky TVs where resonances and rogue RF signals wreak havoc on performance. I’ve always have had trouble with these “Ghost in the Machine” sets.

True, I have found it to work better on chan 7 than 3.
My FADA 895 has been giving me very little trouble , just the odd annoying once in a while.
The horizontal sync has been extremely stable, rarely have to touch the adjustment on the back, only when really cold weather hits.

Only when cold weather hits? God help me!

Yes, sometimes summer vs winter, when it's really cold, the horizontal hold control on the front won't bring it in sync, and have to make a VERY slight turn horizontal freq adjustment on the back, like 1/16th inch of a turn, if even that.

Now what’s that all about? How does it being cold outside make a difference when your house is the same temperature as it is in the summer?

Now what’s that all about? How does it being cold outside make a difference when your house is the same temperature as it is in the summer?

Not quite, I have it set up with the back facing the north wall, and it summer, AC is set to about 77/78f and in winter, heat is set to 65f. :P