CTC-16 Restoration

[Zsuttle]

I've been slowly working my way through a CTC-16 that I picked up several weeks ago. The picture tube tested strongly, and all but one of the tubes were RCA tubes. All but a handful of tubes checked out and were replaced. I replaced the electrolytics as 2 of the 3 cans had a fairly high ESR. There was a corroded wire that was replaced on the topside of one of the boards.

I had excessive HOT current, and was able to bring it within spec by replacing several out of spec caps in that section. I was then able to adjust it to spec. HV is still on the low side (20kV) and have yet to look into that.

I put a test pattern generator on channel 4, and was able to get a somewhat fuzzy attempt at a colorbar. I believe it to be a chroma issue, but have not looked into it other than verifying the presence of the chroma oscillator at the chroma synce phase detector input.

Any advice is appreciated in troubleshooting this set

[old_tv_nut]

Your color oscillator is unlocked, but it's not time to worry about that now. First turn the color down and work on getting a good black and white image. It looks like the picture is out of focus, probably related to whatever is causing the low HV.

[Zsuttle]

I was able to work on the chassis tonight and found several more out of spec resistors in and around the horizontal area as well as many of the 5% cathode resistors. After doing so, I was able to get my HV to max out at around 24.5kV and lowered it back to 24kV.
I'm still unable to focus anything. The focus control does nothing noticeable when turned. Both the HV rectifier and the Focus rectifier are new drop in solid state replacements.

Just to check, the boost voltage just provides screen voltages?

[old_tv_nut]

How about using your HV meter to measure the focus voltage, starting at the CRT and working back?

[damen]

As a test, pull the focus rectifier while the set is on. If the screen stays lighted it usually means the 47 or 66 meg focus resistor is bad. A bad resistor can cause the coil to have little if any effect on the focus. If the screen goes dark as soon as the tube is pulled, the resistor is probably okay.

[Zsuttle]

Ok, here's what I've checked. The focus output to the CRT is 4.3kV, which doesn't change with the focus adjustment. Junction of the 66meg resistor checks out to be 4.56kV.

I pulled the focus rectifier was running, the screen stayed lit. I checked the 66meg resistor, it was reading 64.5meg with a megger at 1500V.

Also, horizontal position pot is shot. Track measures 10ohms, but the wiper is intermittent. Cleaning didn't help. Any suggestions on a replacement? I can find ones rated up to 500V, but nothing over that

[damen]

The RCA part number for the centering control is 113381. The ETF has them, also check with Moyers and Talon Electronics. Check and see if the focus voltage varies with the CRT socket disconnected when you adjust the coil.

[Zsuttle]

Thanks for the PN, for some reason I had another number that wasn't showing up anywhere. Ordered the part.

Focus at the socket was reading 4.25kV with the tube disconnected, didn't change when the control was adjusted.

For my sake, the focus control should only turn about a turn?

[damen]

The 113381 is a new number RCA used to replace several similar controls. It also replaces the vertical centering control when you remove the plastic shaft it comes with. The focus coil should turn maybe a dozen turns running the coils slug in and out. Check and be sure the slug is moving, I've had them detach from the shaft. Also make sure none of the wires have broken off the coils terminals because it does move around when the shaft is turned. If you have the socket unplugged from the CRT, check and see if you get any voltage on the focus pin on the CRT base.

[Zsuttle]

Well that'll about do it. Focus control was jammed, unjammed it and now I'm able to properly focus. Now I just need to narrow out my color issues. Not entirely sure where to start. Is there a nice guide for proper adjustment of a TV from scratch? I know a lot of service manuals cover purity, convergence, cutoff, etc. Didn't see that in the SAMs for the CTC-16s

Also intresting note, the red screen control really drives up the horizontal output current. The blue and green screen controls don't do that. Is that entirely normal?

[kvflyer]

Originally Posted by Zsuttle

Well that'll about do it. F...

Also intresting note, the red screen control really drives up the horizontal output current. The blue and green screen controls don't do that. Is that entirely normal?

Could that be because the red phosphorus is less sensitive and needs more drive to illuminate it?

[Zsuttle]

Could be with the phosphorus, I'm wouldn't be the one to know.

I was able to scope out the waveforms on the schematic in the surrounding areas. Maybe someone can catch something I'm not seeing.

Chroma sync phase detector:
20240809_111223.jpg

20240809_111330.jpg

20240809_111159.jpg

Chroma bandpass amp:
20240809_112708.jpg

Color Killer:
20240809_112921.jpg

Burst amplifier:
20240809_110904.jpg

Edit:
Photos don't seem to be appearing for me, if anyone else can let me know if they see them

[Alex KL-1]

Not able to seen the photos directly; I need to click in the "link", and input again the VK credentials, for each one.
LATE EDIT: after that, all the photos appeared in the post.

[old_tv_nut]

What is the color problem you are trying to chase? Color still unlocked?

I don't have a reference for the color killer and burst amp waveforms, but I would have expected a pulse waveform that is more clearly coincident with the burst, while this seems to be triangular with its peak during active video. What happens to the timing if you move the horizontal hold a bit clockwise or counter clockwise?

[Zsuttle]

Color is unlocked, the waveforms I took were the waveforms called out on the SAMs. Got it from the ETF website. A paper copy is still on order as some things are difficult to read.

Horizontal hold will shift the whole image sideways either direction before losing the horizontal lock. It didn't appear to make any difference on the chroma oscillator. I'm pulling the chroma oscillator from the cathode of the chroma sync phase detector V19