1958 RCA 14-PD8057 Horizontal Issues/Circuit Board Nightmares

[Chris K]

It is a jumble. Sorry for describing it as slightly distorted. That's the way it was before the waveform core broke and I substituted it with a direct replacement from...oh I can't remember who...Merit I think. But I'm sure I installed it correctly. I have my video generator on crosshatch and I've seen this sort of scrambling before and I could tune it in with horizontal adjustments like frequency, hold, lock etc. I think it does lock. I can get it to a point where dashed horizontal and vertical lines don't move...it's just not a picture of a crosshatch. As I said, the waveforms on the scope are perfect.
They are a little jumpy but they are the correct shapes. About 13-14 kilocycles.

[Penthode]

The oscillator will double trigger and cause a jumbly picture if the stab coil is mistuned. Short it out then tune the oscillator to the correct frequency. Then we can fix the stab coil tuning. Or decide whether to again use it as it is not very necessary and may offer improvement if you leave it shorted.

Synchroguide sets were notorious for top of picture hooking when playing a non-timebase corrected VHS to it. Leaving the stab coil shorted may offer some improvement.

[Chris K]

Originally Posted by Penthode

The oscillator will double trigger and cause a jumbly picture if the stab coil is mistuned. Short it out then tune the oscillator to the correct frequency. Then we can fix the stab coil tuning. Or decide whether to again use it as it is not very necessary and may offer improvement if you leave it shorted.

Synchroguide sets were notorious for top of picture hooking when playing a non-timebase corrected VHS to it. Leaving the stab coil shorted may offer some improvement.

So stab coil=horizontal waveform coil L24? Stab short for stability?

[Yamamaya42]

Originally Posted by Chris K

So stab coil=horizontal waveform coil L24? Stab short for stability?

L25, as stated on page 13 of the SAMS, then try to tune L24 horizontal hold to see if you can get it to 15.75k and correct lock.
if it won't something weird is going on.

[Penthode]

Originally Posted by Yamamaya42

L25, as stated on page 13 of the SAMS, then try to tune L24 horizontal hold to see if you can get it to 15.75k and correct lock.
if it won't something weird is going on.

I agree. It should be able now to reach 15.75kHz without the double triggering business. If it is still low, there is too much coil inductance/capacitance in the tuned circuit.

As the slug leave the core, the tuning will go upward. Try adjusting the slug out and see if it reaches 15.75kHz.

[Penthode]

Originally Posted by Chris K

So stab coil=horizontal waveform coil L24? Stab short for stability?

Yes stabilization. It's purpose was to provide minior noise performance improvement and was a feature added first in the 1948 RCA television line.

[Yamamaya42]

SAMS says this is a sub for the Osc coil, if you need it.
https://www.ebay.com/itm/396641916933

[Chris K]

Bought it regardless!

[Chris K]

BTW, I did not have the waveform coil shorted but I did turn the horizontal hold/oscillator (L24) while my scope was connected to W11 and got the waveform shown, was able to alter its shape but got very little change in the frequency...not close to 15.75

[Yamamaya42]

The weird thing is, you should be able to hit 15.7khz and a comfortable margin +/- with the horizontal waveform coil jumpered (L25), by adjusting L24, as we have been saying, why you are having trouble is the head scratcher!

[Chris K]

Originally Posted by Yamamaya42

The weird thing is, you should be able to hit 15.7khz and a comfortable margin +/- with the horizontal waveform coil jumpered (L25), by adjusting L24, as we have been saying, why you are having trouble is the head scratcher!

I haven't tried to tune the oscillator with the waveform coil shorted yet but no luck changing it much from where it sits anywhere near 15.75 with L25 in circuit. I don't know if that would make a difference. Will it?

[Yamamaya42]

Yeah. agreed, the severe ringing in the video is the source of the problem, until you can nail down the source and fix it, you will never have a clean lock, like EM suggested, if you could somehow feed in a cap coupled composite video signal at point B, right after the video det, it would rule out the IF section as a source of the problem, but it looks like it needs to be about 6v P-P (ref W1) to do any good.

[Chris K]

I can do that. I have a B&K 1077 that produces composite video to troubleshoot the video circuit from the video amplifier backwards. I’ve used it before to run down faulty components IF by IF stage.

[Yamamaya42]

Then I guess the next thing is to feed in a video signal at point B and see if you get a better result or not, my guess is that you will.

[Chris K]

Hi all...yes I did. Sorry for the blanking on the camera. I fed in a 45.75MHz video signal at test point B and got a fair picture. It needs adjustment to get it perfect but none of the ringing I had before. It's fine in person but lousy in the camera.