RCA 621ts Restoration

[miniman82]

Looks like the vertical is not locked, and it's got a sine wave rolling through it. Scope the sync section, see if you can catch the sine wave. Could be a heater/cathode leak or short.

[Electronic M]

The video reminds me of when my 1953 Zenith had it's vertical working at double frequency.

Have you made sure all resistors in the vertical are in tolerance? Those can really louse things up if they have drifted too far off value.

[vts1134]

Originally Posted by Electronic M

The video reminds me of when my 1953 Zenith had it's vertical working at double frequency.

Have you made sure all resistors in the vertical are in tolerance? Those can really louse things up if they have drifted too far off value.

I have gone through the resistors in the vertical. I even drew the circuit out as I worked through it. That of course is no guarantee that I didn't miss something, but they all tested within 20%.

[miniman82]

Have you considered an H-K short in the CRT?

[miniman82]

Occam's Razor: you've been making cap upgrades which means you've been messing with the wiring, find the wiring fault and repair it.

[old_coot88]

Finding the wiring fault can be fun and challenging if you make it so. Also helps a Noob hone his skills. Sorta like in the old days an electronics instructor would deliberately introduce a fault into a piece of gear.

[miniman82]

Originally Posted by miniman82

you've been making cap upgrades which means you've been messing with the wiring, find the wiring fault and repair it.

Not tooting my own horn or anything, but I had a feeling that was the problem. Can't blame yourself though, I frequently find errors in schematics so it's not a very big leap to assume something was misprinted. Glad you found out what was causing the issue, pic looks great from what I can see.

[miniman82]

Tell me about it. When I went through AE 'A' school in Pensacola, I was forever finding faults with their trainers. Then again, they were as old as most of our sets...

[vts1134]

Check your work young student! Good advice for every restoration and I should have done it sooner. I traced every wire on every connection that I had my hands on and three hours later I'm vindicated but sad to report that I have not found a single wire/connection out of place.
I tried a few taps on each tube and no changes there. Maybe I can retest the tubes for HK shorts.

Originally Posted by old_coot88

So.. it kinda looks like the hum is arising somewhere in the video chain 'upstream' of the CRT. And since the sync is affected too, the hum must be occuring upstream of the sync take off point. (Just guessing, but the sync may be picked off at the vid. output which was common practice in the old stuff.)...
If it ain't a tube, maybe you could post a pic showing the video amp and sync areas of the schematic.

It looks like the sync is taken off of the plate of the 2nd video amplifier. The video at this point carries the sync pulses with it to the sync amplifier which would magnify these signals. The sync separator would remove the sync pulses from the video (or does the term "separate" come from separating the horizontal pulses from the vertical?) and pass them on to the vertical and horizontal output sections. If this is correct and the problem is originating in the video section, is there a way to isolate every thing upstream from the 6SN7 sync amp/separator to quickly confirm this? Would removing the video amplifier tube achieve this?
I could be completely off base on my thoughts above but just trying to think it out as much as I can on my own so I can learn.

[miniman82]

Originally Posted by vts1134

is there a way to isolate every thing upstream from the 6SN7 sync amp/separator to quickly confirm this? Would removing the video amplifier tube achieve this?

You can isolate everything from before the video amp by lifting the grid connection (V105 pin 1), then injecting composite video right into the video amp on pin 1. If the problem goes away, the issue is in the tuner/IF. If you remove the sync tube, the picture won't lock at all and I think it would be difficult to tell if there problem were still there or not.

[vts1134]

One last thought.
If the problem is coming from the video section would it still manifest itself with no video signal present?

[old_coot88]

Originally Posted by vts1134

One last thought.
If the problem is coming from the video section would it still manifest itself with no video signal present?

Yes it would, assuming the raster has still got that heavy white bar in it. That bar's still present, right? If it is, there's another trick you could use that doesn't involve lifting any connections or injecting a signal (the bar is the "signal"). Get that trusty .1mf cap again* and hook one end to ground, and the other end to a clip lead. Starting with G1 of the CRT (this set injects video via the grid instead of the cathode), and connect the cap to it. This shorts the signal and should produce a blank or near-blank raster. Then take the clip lead and progressively work back, shorting the plate of the 2nd video stage, then the grid, then the plate of the 1st video, then the grid, and on back through to the plate of the 6H6 and then the cathode. If at any point the bar remains unaffected, you'll know it's originating in the stage you just left, 'downstream' of the shorting cap.

Be sure and discharge the cap to ground after taking it off the plate of a tube!
-------------------------------------
*If the single cap is not killing the bar sufficiently, and if you have more than one of those .1 caps, put as many as you can in parallel to get higher capacitance for better shorting effect.

[DavGoodlin]

Oldcoot88: "Is that coating securely grounded? An ungrounded or poorly grounded 'dag can cause some really weird symptoms mimicking sync and AGC problems (a little factoid worth bookmarking)."

Good one! A spring arcing in a curb-found 1961 Philco BW, left the room, and the CRT "blowed up". Made a hell of a mess out the back. Cant be too careful grounding.

[old_coot88]

Originally Posted by DavGoodlin

...A spring arcing in a curb-found 1961 Philco BW, left the room, and the CRT "blowed up". Made a hell of a mess out the back. Cant be too careful grounding.

Dang. First time i heard of that happening (other than those SS color Zeniths with the 4-legged Safety Cap which would fail, letting HV soar to over 50KV, cutting the neck off the picture tube).

[Electronic M]

LOL. Here is a clue on that aqua dag check. If you use the grounded screw driver CRT technique to discharge the HV, then use the same tools set up the same and with the set on touch the blade of the screwdriver to the aquadag coating in a few spots and if you get an arc or spark then the CRT's dag ain't properly grounded. Might also be able to use a HV meeter instead of a screwdriver.

Awhile back I accidently confirmed I had this issue on my CTC4 with my hand.....it shook me up and made me swear like a pirate. 25KV can certainly alter ones vocabulary and mood.