1958 RCA 14-PD8057 Horizontal Issues/Circuit Board Nightmares
 

Hi folks. Working on one of these very popular B&W portables. I've restored and sold several but this latest project is giving me some fits to say the least. Anyone who has worked on one of these knows the circuit board was not designed with service in mind. It's mounted and shielded like a bank vault. The board itself is grounded in six places to the chassis frame it sits on...the 4 corners and for good measure, a spot in between on the 2 long sides. Additionally, there's an RF shield about half an inch under the board covering the entire thing that's screwed to the mounting frame and has almost inaccessible tabs soldered to points on the traces of the circuit board in 4-5 places. There are some access openings but they are not solder iron friendly for sure. Removal of the CB is not a practical thing to do given it's situation and the soldering and presence of many wires on the top of the board. For this reason, most of the work I do on these TVs is top of the CB component replacement. The power supply is so much easier to service.

So given this, the TV has a NOS 14ATP4 CRT that's bright and crisp. It has issues with a jumpy and distorted horizontal circuit so I was attempting to adjust it by turning the core in the horizontal waveform coil mounted to the dreaded CB. Just as I was getting close, the core crumbled. I was able to get a NOS Miller 6337-R direct replacement for it. I think I'm just going to clip off the broken coil and solder the new one in by attaching it to the metal tab remnants on top of the board instead of diving into hell on the underside.

Stay tuned. I'm all but certain I'll create more issues than I solve!

Good luck, somo old PCB are really fragile, besides the dreaded chassis tank-like-soldered as you said...

Thanks...already have an issue! The NOS coil has 3 tabs like the original. If I'm reading the description that came in the box and looking at the coil itself, tabs 1 and 3 are the ins and outs of the coil winding. What would tab 2 be...a ground??? I don't see that depicted in the schematic. Anyway, here's the schematic of the horizontal circuit part where the waveform coil resides.

https://imagizer.imageshack.com/v2/1...924/wqPA3M.jpg

So from the looks of it, I connect pins 1 and 3 to the leads going to the 0.01uF capacitor on the board?

I did this and now...no picture or horizontal signal. I checked it at the horizontal hold control with my scope and nothing. No horizontal waveform and no picture. Now, as most of you know, this is probably an idiotic screw up on my part...a tube knocked loose, a bad solder joint etc....Before the replacement of the waveform coil, I had a picture that was sharp and bright, just unstable and distorted horizontally

I guess my question is could a mis-wired waveform coil completely eliminate the horizontal signal coming out of the oscillator or should I still have the signal at W11 even if it's not wired correctly or is missing? If it could affect the horizontal signal from the 8CG7 and I remove the new coil, should I get a double peaked horizontal trace at W11 and does removing it seem like a good troubleshooting strategy?

looking at the paperwork from the box, pin 2 = NC , No Connection, so it's just there to keep the thing stable.
https://www.ebay.com/itm/195881922845
You should be able to do a resistance test from pins 1-3 on the new in circuit and it should be rather close to the one that was removed.

I did...it ohmed out at 50 ohms between pins 1 and 3. Schematic says 48ohm. I think I did something stupid. I'll go back to basics tonight and make certain the tubes were put back in the correct sockets, that they didn't get messed up internally, seated well...that kind of stuff

BTW, that's my purchase you see in the eBay link! I've bought a number of NOS RF and IF coils from him in the past. Pretty impressive stock.

If you look at page 23 of the SAMS, where is has the horizontal oscillator sweep setup, the first step is to put a jumper across that coil, and since the plate of horizontal oscillator gets power (P6) through that coil, it wont work without it, but will if has a jumper.

Great!!!! Once I eliminate the "stupids" from troubleshooting, I'll try that.

I'm assuming you have the schematic. If not, I'll post more of the area. The plate of the oscillator gets 175V DC through the waveform coil. Is the drop from 275V to 175V facilitated by R92...the 56K 1W resistor? Just for my education!

Yes, as far as I can see, the current path for the Horz Osc V12 pin 6 is R92, up trough L25 (48 ohms), and L24 (20 ohms).
using. https://www.earlytelevision.org/pdf/...sams_396-3.pdf :D

OK thanks. Me too, using 396-3 from the ETF.

Broken trace. Fixed with a jumper. Waveform looks perfect but, I'm only at around 13KC not 15.75 and I can't get the horizontal dialed in. Vertical locks and is fine. Distorted and wild messed up crosshatch off my generator. Three adjustments in the horizontal circuit...width, waveform and horizontal hold. Maybe the oscillator is weak. I'll test it.

EDIT: Looking at the caps in the horizontal. There are 3 mica caps, 2 at 1000pf (C99 C100) and one at 330pf (C98). I didn't replace any of these but someone did replace C99 with a 5% cap but not a mica...at least not that I can tell. It It's a rectangular cap like one of those safety caps and says CD Type Made in USA 5 Amps on the top...5% and "D" printed in quotes on the face. There's more including the uF but there's a bunch of crap in front of it and I can't see it. Definitely not what's depicted in the photo of the board in the Sams.

Why am i having this sudden feeling of dejavu?
cause I just went trough this with my maggy? :D
C99 looks like it may be just a decoupling capacitor, not sure.
Critical one are C94,C95,C96,C98 and the resistors in the area, C93 passes the sync pulses down from the sep amp, so if it's not right you won't have lock or weak lock, C100 passes the signal to the output, the problem is prob in a the AFC area, if the caps or resistors are bad / out of spec, it's not allowing the PLL circuit to work correctly and thus out of frequency.

Not to fixate on C99 but I was able to move things around a bit and it looks like the cap is a 0.01uf cap and not 1000pf. C93 on my CB is a ceramic cap but I can't make out the rating. Supposed to be 82pf. I do have an 82pf mica I could substitute for it. I really don't have any way to test the ceramic. Externally it looks fine. There is another ceramic next to it that's not in the Sams Photo or component list so there might be different versions of this model.

https://imagizer.imageshack.com/v2/1...924/ER8Xm6.jpg

Actually I can see the 82 in the photo

This is where it's good to have a LCR meter. :D
It's said that ceramic disc capacitors for the most part never go bad, but they also say never say never!
You would be more likely to find a dodgy resistor than a disc cap, but you never know!

What do you think would be the implications of C99 being a 10,000pf cap instead of 1000pf? If it wouldn't make a difference, I'd like to minimize how much work I need to do under this board. I'd just as well leave it there if it makes no difference.

it may have something to do with the sawtooth shaping, not sure, but if that's what they got in there. :D

I think there's a chance RCA didn't put it in there. The Sams shows a 1000pf in the capacitor list, schematic and it looks like the board photo is of a mica cap.

At this point there is no way to know, there should be clear evidence that someone has touched it before, disturbed solder joints vs OEM, joints, if it does look like it was replaced, you have nothing to lose by trying what's on the SAMS, but this also can be a case of an update after the SAMS was made, if it makes it worse, it's not like it will go FOOM right away, it just won't work any better.

I had trouble with a synchroguide circuit once and it turned out to be a 330K resistor had gone sky high.
Here's a tutorial on the synchroguide circuit:
http://rca.vobj.org/RCA%20Engineer/R...ignHistory.pdf

Thanks! The resistors in the circuit I've tested so far have been close to the stated value. The tearing in the upper part of the picture in the RCA tutorial is exactly what I'm seeing.

Still no joy on this project. I’ve checked all the horizontal waveforms at the test points and they all look the way they’re supposed to look. Frequency still low at 14KHz. I changed a 120pf original capacitor in the circuit and it’s better but not right. There’s a couplet in the AGC circuit. Could that be affecting the circuit?

From what I understand, the horizontal oscillator should be able to free run at 15.7khz approximately without any external influences, IE, no rf signal or anything, the incoming video only keeps it locked in step as needed to hold the picture to be seen, so that circuit before the horizontal oscillator (couplet), really should not be having any effect for you to tune it to 15.7khz, something else weird is going on.

I agree. I think I'm going to have to go down the rabbit hole and at the least, partially remove this circuit board and look at the traces and grounds. Ugggggh! I've been watching CuriousMarc's channel obsessively for the past month and maybe I need to take their approach...detailed analysis and then dive in. If they can reverse engineer Apollo core rope memory literally stored on bundled wires, maybe I can troubleshoot this board.

The truth is in the whacked picture but maybe I need to evaluate the frequency on another scope. I'm using my HP digital which has always been accurate when assessing frequencies.

https://imagizer.imageshack.com/v2/1...923/VMn5Kx.jpg


The waveform at this point is easily manipulated by B1 and I have it dialed in to the exact shape seen here. I also have a sawtooth waveform at W12 but, again, the same off frequency signal. I'll play around with it tonight and double check for idiot based errors. The tubes test good and I have switched them with known good tubes, the tube sockets are OK and the 5% and 10% resistors are in tolerance. :scratch2::scratch2::scratch2:

But again, I'll see if I did something stupid.

Coming to this thread late. Have you tried for trouble shooting shorting out the stabilization coil? It appears to be called Horizontal Waveform here and a short can be placed across the 48 ohm coil. Then you should be able to first adjust the horizontal hold coil to sync.

If with the other coil shorted you cannot get sync then something in the circuit is at fault. But that would be my first step tackling this.

I want to add that I left the stab coil shorted in my RCA Victor portable. It improves VHS tape playback performance (less bending at the top of picture) and it allows me to easily adjust the oscillator to 10,125Hz for UK 405 line display.

The stab coil was only introduced to marginally improve noise performance on very weak signals. Feeding modulators with strong signals it accomplishes nothing today

So, one should be able to get a 15.75khz shark fin waveform at point W12 with the frequency being adjusted significantly by L24, above and below 15.75khz, and having Horizontal Waveform shorted or not should have little effect on this.
However, influence from the sync amp given that it's tuned to a good video input, will adjust the oscillator to some degree.
I just find it a bit odd that you say that it's running at 14k, cause if it was that low, would there not be any lock at all and just a jumble on the screen horizontally?

Some screenshots would be useful. I would like to see the stab coil shorted and screenshots as it is tuned to sync.

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.

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.

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

Bought it regardless!

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

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

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?

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.

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