Ctc-7aa - Page 4 - Videokarma.org TV - Video

Electronic M · #1 01-02-2012, 05:02 PM

"Now, I'm going to take a break and watch the Badgers in the Rose Bowl... "
I can relate to that...just got a my CTC4 to display video an hour of two ago and had to watch it for an hour no color, poor focus, lousy purity, poor convergence and all. When a rare set comes back to life for the first time in decades ya just got stand there in awe.

stromberg6 · #2 01-02-2012, 05:28 PM

Another 4 brought back!! congratulations!

Electronic M · #3 01-02-2012, 07:44 PM

Thanks! I got a thread going in this section of the forum if you want to see how it is comeing along.

kvflyer · #4 01-02-2012, 07:47 PM

Very nice. I wish I could just drop everything and work on my "stuff". But my CTC-9 is 737 miles away waiting for me to move to Florida. Can't wait...

IsthmusTV · #5 01-08-2012, 12:40 PM

I'm continuing to recap the whole chassis in stages. I also finally tested all the tubes and found a bunch that were weak, shorted or gassy and replaced them. I also carefully cleaned the tube sockets and the tuner with DeOxit applied with toothpicks and Q-Tips. The set now produces a very stable picture. (I still need to get my hands on a degaussing coil):

I decided to try a rough adjustment to the convergence, which was really bad. Things went pretty well until I got to the horizontal dynamic convergence:

None of the horizontal convergence controls seem to have any effect. Clearly, there is something amiss. I haven't begun to trouble shoot yet, as I thought I'd check in here first for advice. Any common failures to check out first? I wouldn't be surprised if the selenium rectifier is bad.

Thanks in advance.

-Clark

Phil Nelson · #6 01-08-2012, 01:24 PM

Wow, that picture is really shaping up. A bad selenium rectifier on the convergence board would not be unheard of. On my first CTC-11, when I unsoldered the legs on the selenium unit, it fell completely to pieces.

Before it was replaced, simply touching the old rectifier, or the board nearby, made the picture go nuts.

I installed new fast-response diodes that someone sent me. I don't have the type number at my fingertips. Perhaps it is buried in a past thread.

No guarantee that this will cure your problem, but the parts cost almost nothing, and selenium rectifiers are so sketchy that I routinely replace them in radio restorations, just like electrolytic capacitors.

Phil Nelson

Ampico-kid · #7 01-08-2012, 01:43 PM

I don't claim to be an expert with convergence, but the first thing that jumped out at me when I saw your picture is that it appears the static convergence is off...most notably the Blue lateral adjustment. This is the control on the neck of the crt closest to the socket that moves the blue beam left and right.

I would guess that you haven't tried to perform a full static convergence yet. Using a Dot/Bar generator and set to dots, the goal is to end up with a pure white dot in the center of the screen, using the three static convergence magnets on the neck of the crt. The Blue lateral is also used to obtain that white dot. Once you've got the center white dot the rest of the screen is converged using the Dynamic convergence controls on your convergence board.

I've never seen a perfectly converged vintage color TV. I think the goal is to get it as good as you can and be happy with it. It most definitely does take some artistic and creative maneuvering to get the picture to look good since many of the controls interact with each other.

I would say if you can sit at a distance of about 6 ft. to 8 ft. from the screen and it looks good...you've succeeded.

Hope that helps......
Bob

Steve D. · #8 01-08-2012, 02:20 PM

You really need to get your hands on a degaussing coil and start the purity process before attempting any serious convergence procedures. Other wise you'll drive yourself nuts and get very frustrated achieving that "perfect" convergence.

-Steve D.

IsthmusTV · #9 01-08-2012, 02:49 PM

Thanks, Phil, Steve and Bob, those are all good suggestions. I did try static convergence first, and I could get the blue dot to move only so far. The lateral positioning magnet did have a large effect on the static convergence, but it's very loose when I rotate it. Is is possible that I need to reposition the convergence yoke?

I think I'll back off for a while until I get a degaussing coil and can preform the purity adjustments.

-Clark

miniman82 · #10 01-15-2012, 02:32 PM

On the crosshatch pattern, see how right after every horizontal line there's a little hump in the vertical line? Your horizontal wave shaping coil needs to be adjusted, that's the step in Sams where you scope the coil and turn the slug till you see equal humps.

IsthmusTV · #11 01-16-2012, 09:14 AM

Hi Nick,

Thanks, that makes a lot of sense. I'll give that a try.

I think that some of the edge purity hairpin magnets are missing. There is only one hairpin magnet at three of the locations on the right side of the CRT whereas there are two at each location on the left side. Are these things hard to come by?

-Clark

miniman82 · #12 01-16-2012, 12:47 PM

Hairpins should be easy to find, pair them up as best you can and don't leave single ones or they will affect the purity.

IsthmusTV · #13 01-24-2012, 10:22 AM

Well, I've suffered a bit of a set back. I tried adjusting the horizontal "sine wave" coil per the RCA service manual. I attached my scope to test point "E" as instructed, but the waveform appears to be the horizontal drive output, and not the the other waveform. In any case, turning the slug in the sine wave coil did not affect the waveform or the picture. Here's a shot of the waveform that I got:

I don't know whether the RCA service manual misidentified the test point or if there's another problem. As time went on, I was having more and more trouble keeping horizontal lock. I also found that the horizontal hold control (which is actually the horizontal oscillator frequency control) had to be maxed out in one direction to achieve lock. I tried readjusting the sine wave coil, but it again seemed to have no effect.

Eventually, I was unable to get horizontal lock at all. I powered the set down for a while, and when I powered it up again, I got no raster and the HOT started to red plate. I knew that I still had a bunch of maroon drop caps left which I thought might be the problem, so I pulled the chassis and changed out about 10 more, including those on the video amp/AGC board. When I powered up again, nothing had improved, the HOT red plated and no raster. I'm assuming that I must have lost horizontal drive, or that the horizontal frequency is way out of whack. I tried subbing tubes, and when I put in a NOS 6AU4 damper (even the the old one tests good) the HOT no longer red plated, but I still had no HV or raster (I also tried subbing a NOS 6DQ5). I'm not sure what that means. I inspected the fly, and I don't believe that it's the problem. The only caps left on the horizontal board are two mica caps which I didn't have replacements for. I am still pretty much a novice at this stuff and I'm not sure what to do next. I'm afraid of screwing something up. Incidentally, I never let it red plate for more than a few seconds.

I'd like to be able to power up just the chassis on the bench, but I assume that that would not work without the deflection and convergence yokes attached. I may see if I can power up the chassis with everything connected but the chassis propped up behind the cabinet. That would allow me to finally measure the HOT cathode current. Anyone know if that's possible? I'm feeling a bit frustrated at the moment.

Thanks for any advice,

Clark

DaveWM · #14 01-24-2012, 10:47 AM

looks like you have a .1 not a .01 on the sine wave cap. Better make sure you are reading your cap values on the replacement correctly

DaveWM · #15 01-24-2012, 11:00 AM

did you check under the IF cover for any bumble bee caps? there is a .01 in there that couples the noise invert to the sync sep, seems like it could cause issues with sync.

I am going thru a CTC-9 now. What I do for what its worth is lift one leg of a cap, and use an old school cap tester. If the cap test bad, then I replace it, but before doing that I take the new cap and put it back on the cap tester.

Most of the time the old caps leak but you can get some indication of the value on the cap tester. By leaving all the settings alone, and trying the replacement cap on the tester, you can do two things, verify the value of the replacement and verify the replacement it good.

This step avoids 10x order of magnitude errors and finds the bad new caps. I have had a few of those yellow caps shorted when brand new.