1958 RCA 14-PD8057 Horizontal Issues/Circuit Board Nightmares

[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.

[Penthode]

Did you move any leads or change any components in the IF amplifier? Any lead dress changes?

Any change to the connection between the tunerout and the first IF stage? Any changes to the shielding?

If all looks good or you insist there has been no or minimal wiring changes, have you tried substituting the IF amplifier tubes? I recall this set has 3 IF stages. My preference is to first determine which stage may be or if is mistuned. Assuming it uses exposed bi filar wound coils, try maneuvering a metal screwdriver tip near each coil while watching if the ringing changes.

The video carrier is typically at the 50% point on the response slop at 45.75MHz. the tuner mixer out to first IF and the 3rd IF Amplifier to detector stage both are typically tuned to 44MHz or thereabouts. The stagger tuned stages from around 43 to 42.5MHz will lie in between. If one of these stages becomes mistuned towards 44MHz, regeneration may occur. So try detuning some of the stages slightly only with the steel blade of a screwdriver gently near the coils and watch the result.

I don't think the tuner can cause this as the RF bandwidth is broad. But lead dress eg even location of the antenna lead to the RF input near an unshielded IF stage may cause regeneration.

[Chris K]

Thanks so much for your thoughts and guidance. I'll answer your troubleshooting questions one at a time. I'll preface this by saying the TV was in original condition when purchased. My restoration has been limited to component replacement. The 120V AC fusible resistor was bad so I mounted a fuse holder and the inch or two of wiring necessary to facilitate its mounting. That's the only change to the original wiring I have made so if there are lead dress issues to be found, they would be in the factory wire length and routing and not in any changes made by me. So to answer questions regarding wiring out of the tuner, wiring in the IF section, shielding of tubes etc...everything is as it was. The IF tube shields are adjustable in height to make tube removal easier but they have been extended to full height during all of the process.

I swapped out all of the original tubes with NOS tubes but I've not done extensive replacement troubleshooting, just the 8CG7 and the 8AW8 several times (Horiz Osc/AFC, Video Output/Sync Sep). I'll try the screwdriver probing for changes in the picture but all coils in the IF section are shielded below metal enclosures. The antenna input from the video generator is clipped to the 2 lugs on the tuner case so I could reattach the twin-lead antenna wire and connect the generator to the end of the wire but I've worked on several of these TVs and direct connection into the antenna lugs on the tuner has never been an issue.

I'll try nudging the IF coils a bit and see if that changes anything.

[Penthode]

One other perhaps not so obvious thing is ensure all the soldered grounds to the board are good. Might be useful to resolder the grounds to make sure.

[Chris K]

Originally Posted by Penthode

One other perhaps not so obvious thing is ensure all the soldered grounds to the board are good. Might be useful to resolder the grounds to make sure.

Absolutely will do that. There are about a dozen solder points including several running from the bottom of the circuit board to the shield under the board.

[Chris K]

Originally Posted by Penthode

One other perhaps not so obvious thing is ensure all the soldered grounds to the board are good. Might be useful to resolder the grounds to make sure.

At least 3 shield ground tabs were loose on the bottom of the board. I still have to do a few more checks but it's 85% better. P'Thode my friend...you're a life saver! Gonna take a break from this tonight and align my Zenith TO. This RCA is wearin me out!