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.

[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

[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]

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]

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 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.

[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.

[Chris K]

OK...UPDATE

With the L25 stab coil untouched, I get the following: FYI, 10X on probe...1X setting on scope so the voltage P-P is 140V DC








With L25 shorted and the oscillator adjusted:







So I'm close to frequency now with a better picture but it's still pretty bad.

[Penthode]

You have severe ringing in the video. Looks like an open decoupling cap, bad shielding of an IF amp tube, lead dress. The ringing in the video will affect horizontal sync. The ringing looks to be at a few hundred kiloHertz. There are some simple remedies we can discuss later. Fortunately the alignment of this set is a whole whole lot simpler that the 1940's chassis. Lol.

Have you tried adjustin the fine tuning? Or tried another channel?

But it looks like you have serious video channel problems.

[Chris K]

Yes I've tried several channels and ran the fine tuning through the full range. I replaced all film caps that were on the circuit board including a few mica caps and an 82pf ceramic in the horizontal circuit.

Is the resonance why the chassis has this pain in the butt shield under the circuit board?

[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.