CT-100 restoration questions

[John Folsom]

I agree with Steve. I have never seen any of the lower voltage doorknobs assockated with the focus or convergence circuits go bad, though I have had several of the 30KV doorknobs in 15" color sets fail. They did not hurt anything else when they failed, as the HV rectifier tube provides som isolation. But like the filament windings and convergence transformer, I now replace the 30KV doorknob with a "modern" one. There seem to be plenty of 30-40KV doorknobs available on ebay these days.

[Tim]

Hope everyone had a great Halloween. After the trick or treaters quit ringing the bell, I grabbed a Peanut Butter Cup and decided it was time to put some volts to the chassis.

Tonight was a meaningful night to do that as it was 50 years ago tonight that I, as a young trick or treater, saw color TV for the first time. I'll never forget when that lady opened her door and there in the living room was a huge wooden TV cabinet displaying a COLOR picture! (CT-100??) I don't think I even knew color TV was possible before that night. It was 10 years later when we finally got a color set.

Anyway, I removed the Horiz Output tube, plugged all of the coils and speaker, connected a few voltmeters and ammeters and started cranking the variac. I think it has been at least 15 years since this chassis had power applied. At about 90 volts I heard noise from the speaker and kept going to 115V. Voltages and currents did not seem out of line. I rotated the tuner one click and there was audio from the newscast! A little rotation of the fine tuning control brought it in perfectly. It is always a great feeling to have a set come back to life but this one feels better somehow.

I shut it down after about 15 minutes. after I took some readings. I noticed that the Field Neut. pot was a little warm to the touch. Not sure if this is normal so I would like some confirmation on that.

Here are my voltage and current readings and would be curious to know how these compare to other's readings. Again, no Horiz output or CRT so these will change.

Line: 115V 3.3A
380: 402V
375: 393V 50ma
285: 291V 275ma
275: 275V 140ma
175: 188V
-30: -23.7

I think I'll grab another Peanut Butter Cup. It was a good Halloween.

[John Folsom]

Tim,
Those voltages seem quite reasonable. The field nertralizing pot carries B+ current, so it will idssapate s bit of power. I think it is time to put the HO tube back in its socket and generate some photons!

John

[Pete Deksnis]

I've missed all the foregoing good stuff sunning myself in South Carolina for the past four days. Great to hear another CT-100 will soon join the operational list. Good luck. Tim, with the attempt. Just keep an eye on the focus voltage either by monitoring the 19.5 kV HV (it takes a 10 kV or so dive when it's in trouble) and/or the 1X2B focus rectifier for stress.

[Tim]

Welcome back Pete. We were in down SC for a week in the summer. Great place.

HO tube back in, power on and we have photons and a steady 20KV of electrons as well! I let it run for about 15 minutes - no snap, crackle or pop. While it was running I fugured I'd put the scope probes on the red, green and blue video outputs and see what there was. I got a recognizable video signal on all three. Seems like I am off to a good start, sound and video.

Pete: What should I be looking for regarding the focus voltage? What is the failure mode or point?

[John Folsom]

Tim,

You should have 3.5-4.5KV on the cRT focus electrode. The only likely sources of failure would be the filter cap on the wiper of the focus pot, or the convergence transformer, both of which you have replaced. So I would not expect you to have focus issues. Have you put the chassis in the cabinet and fired up the CRT? What resultas are you getting?

[Pete Deksnis]

Later on when you monitor the video outputs with a color bar signal input, here's the challenge: check for twice the red drive as the green. As shown in the link of a CTC2 driving a good tube, the red drive (bottom) is about 60 volts vs about 30 on the green video.

http://home.att.net/~pldexnis/CTC2_h...22-60R-30G.jpg

[Tim]

Hi folks:

I have 4KV focus voltage. Red drive is twice the green drive. I do, however, have alignment/IF issues that need to be sorted out as, although I can tune in a signal, the video is very noisy. Audio sounds clean.

I have not put it in the cabinet as of yet as the CRT is boxed up and the empty cabinet is in storage. It needs some refinish work. I wanted to get the electronics working before spending any time on the cabinet. I will probably get it out this weekend.

Stay tuned.

[Steve D.]

Originally Posted by Tim

Hi folks:

I have 4KV focus voltage. Red drive is twice the green drive. I do, however, have alignment/IF issues that need to be sorted out as, although I can tune in a signal, the video is very noisy. Audio sounds clean.

I have not put it in the cabinet as of yet as the CRT is boxed up and the empty cabinet is in storage. It needs some refinish work. I wanted to get the electronics working before spending any time on the cabinet. I will probably get it out this weekend.

Stay tuned.

Tim,

I also had good sound with a very noisy picture on my CT-100. Not exactly a technical fix, but I cleaned the brass contacts on the tuner drum, which were quite dirty with corrosion. Improved the picture dramatically. Give it a shot.

-Steve D.

[andy]

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[Chad Hauris]

Noisy video sounds like a peaking coil issue perhaps.

[John Folsom]

Tim,
If you have a 1V or more composite video source, you can feed video directly to the grid of the 1st vidoe amp (remove 56h IF amp). If you still have noisy video, it is simple to signal trace through to the CRT grids to isolate the porblem. Is the noise only in the Y channel, or is it only in the color portion of the signal? And if the noise clears up when you inject a signal, then as suggested by Steve D., I would try cleaning the tuner before any alignment is attempted. You might also check to ensure the AGC is operating properly.

[Tim]

Evening folks:

Yeah, Alignment is the last thing to touch, I learned that the hard way many years ago but thanks for the warning. The tuner is definitely at least part of the problem so you nailed that one Steve. I injected an IF signal and was able to adjust it so the display on the scope was fairly clean and stable. I then threw a tuner sub in and the signal was greatly improved over the original tuner. Tomorrow I'll open it up and give it a good cleaning. I will then proceed from there. I intend to get the video looking good on the scope before trying to reassemble the CRT and cabinet.

Interesting you mention the peaking coils Chad. Some were, of course, open from the well documented corrosion. I replaced them using the part numbers recommended on Pete's site. I assume these are known to work OK.

I really appreciate all the suggestions and support guys.

[wiseguy]

I have several of those peaking coils N.O.S,that the actual manufaturer sent me as "samples" they had still in stock and sent them to me no charge..they are improved over the wax coated ones originally used in the ct-100, "J.W.MILLER" was the manufacturer i have 2 of the 220 uh,1 of the 1500uh,2 of the 6200uh,and 1 or 2 of the 1000uh,and 5 of the other 2 values used in the ct-100(i cant see the uh,i will have to look up part numbers..)
but you can have all these ,these were left over from my CT-100 restoration,i dont ever see getting another CT-100 in this lifetime..LOL
if you want them then give me your shipping info..
terry

[Tim]

Thanks Terry, your offer is greatly appreciated. Sure, please send them and let me know what you want to cover postage, etc. I will use what I need and pass whatever is left on to the next guy. I'll PM you my address.