I flipped a coin last week over whether to post this on antiqueradios or here; no response there so here I am.

This tv had been in storage for the past 5 or 6 years; when I pulled it out the other day I decided it had been too long since I had worked on a set & this should be the one. When I had last used the tv the picture was just tired looking, poor reception, poor color, poor contrast, etc. I powered it up last week & had a weak picture with messed up color. I kind of jumped the gun & starting swapping 6GH8's all around. (this set is my payback for posting last week that 6GH8's never give me any trouble!) Actually I found most of the trouble was in the agc and after adjusting that & the gray scale I had a very good bw picture. But where did the color go? Since then I have swapped the crystal & the color killer transistor; replaced the filter cap that feeds the circuit along with a burnt resistor in the power supply; tested every 6GH8 in the set & on the shelf & put the best of the best in the set; adjusted the coils per the directions in Sams. I did finally get color back with the color bar generator hooked up. The trouble is that I cannot get it to stay put. Well, it will stand still but tweaking the tint control will send the color bars spinning in one direction or the other. I finally gave up for the night & decided to just hook up the cable so I could at least see a color picture with this set-when I connected it I had a dark, overloaded raster. The agc was too far out, turning it back to get a picture causes the color to go away.

One odd thing that happened: while probing one of the demodulators there was a flash of spark and a loud zzzappp!!! in the area of the 3.58 oscillator. I am almost certain this had nothing to do with my measuring the voltage several inches away. I could see no obvious damage & nothing seems to have changed. I did notice that coil A19 (going by memory here) has no effect on the voltage when I am doing the alignment-I've done no other check & wonder if it could be bad?


I look forward to bringing this set back. Its a remote set, a lot cleaner inside than I remembered. This is the tv I bought from a guy in the mid-90s who was doing bait & switch: come in to see the $5 color tv he has for sale and walk out with the $50 Sanyo instead of this old beast.

I always enjoyed working on the ctc31. I did a total restoration on one I picked up at the curb 2 years ago. Needed the ususal 6GH8 change. When you tested your 6GH8s did you perform a life test on them with your meter? The life test is critical in determining if the tube is going to work satisfactory or not. Also, did you check the tubes for grid leakage? gh8's are known for bad grid leakage, or also called grid emission.
The one set did have weak color and that is simple checking/replacing of the mixer/osc and check your pix IF tubes, those can kill your color, or weaken it. I dont want to rule out tubes just yet, as they normally cure the ctc31 color problems. Should tubes definitly be ok, I have some helpful pointers on aligning those chassis. Since you get color on cable, it sounds like a front end problem.
Keep us posted! By the way, can you show a pic of that set? Remote sets need to be shown! hardly any of those out there!

I have got a CTC 31 that does this sort of thing...the color sync is poor. However mine appears to be a thermal problem, because as the set warms up the color starts drifting less and less until it finally locks in. Have not definitely found out what the problem is, though.

Thanks for the tips. Looks like I may have to test those tubes a little better. I hadn' t spent much time with the IF tubes & will check them as well. Maybe I can get a photo up this week; right now its facing the wall. (pretty heavy to go moving too much, threw my back out getting it in the house) Hey, this is one crowd that appreciates a chassis shot, so maybe thats what I'll post!

If you check your tubes and make sure they are all 100% and still no sucess, your IF has probably drifted. Since you were getting color on cable, I know that your color circuits are fine. There is a sound rejection pot on the ctc31, pictured is the blue color pot. adjust it and your color could pop in. The contacts get dirty on those. Also, after youve adjusted that, the 41.25 mhz sound trap is in seires with the pot, its to surpress the sound carrier, and when those go out of alignment, your color will be very weak and faint. Ive adjusted them before and you would be surprized how much these old color sets drift off over the years. You can simply "eyeball" these coils. The first coil has the more effect than the second. This first 41.25 to adjust is the one just in front of the 6KT6 pictured, the second is the taller one just to the left of it. Adjust for minimum beat while watching a color program, and while you are doing that, you will see the color intensity increase. Watchout, as when you adjust the first coil, you could go to far and have color ghosts.

I did some more tube swapping last night, including the IF tubes, to no avail---funny, I was eyeing that screw, but didn't dare touch it! Gotta make time tonight to try it!

I like to mark the positions of any controls before I adjust them unless I know exactly what they do. That way if it doesn't help, I can return it to its original position.

Just returning from vacation....needed one after working on this set! I tweaked the controls and it did seem to improve the situation though I still could not get things right. At the same time something else happened and it has me perplexed:

There will be a "rapping" noise that will start to come, apparently from the HV section. Coinciding with this will be ragged white lines on the screen, sort of like retrace, and a darkening of the raster. As the picture darkens (this is probably a red herring) the color will appear, if weakly) then the raster (the HV, too, I am mostly certain) will dissappear. Soon it will come back to normal. Sometimes it keeps up the cycle and sometimes it behaves itself for awhile. The only unusual signs I see are: once there was a spark inside the horiz output tube just as the HV came back; on several occasions as it came back there was an ugly blue spark in the neck of the crt. I can make guesses: change of IF frequency has messed something up in horiz osc. frequency (doesn't seem likely) or a bad flyback(I can't see anything happening in there, but hard to really tell) or an internal short in the crt or one of the HV tubes? Anyone care to guess? I'll bet some of you, who really know what your'e doing, will have the answer!

Maybe I'm off base on this one, but I had the same thing happen to one of my sets. Turned out it was an intermittent short in the horizontal output tube. Replaced the damper and horizontal output tubes with NOS and never saw the problem again.

Also I have had this happen when the ground connection has loosened from the CRT. There is arcing from the CRT outer coating to the ground, causing the arcing noise in the picture...if the ground connection comes loose enough, the HV filter capacitance is lost, causing the voltage to drop and the picture to go dim.

Check along the CRT grounding spring...make sure there is a good firm connection between the grounding spring, degaussing shield, and chassis. The main CRT to chassis ground connection is a metal strap that is attached to a corner of the CRT, it contacts the chassis through one of the front chassis mounting bolts.

Chad, you may be onto something, as I had pulled the chassis and it is not bolted down right now-may be no connection at all the way it is? One night this week I'll take another stab at it.

I went to work last night trying to solve the HV problem (for lack of a better term) and things just don't look good to me. First I looked for a ground strap off the crt. There is a metal shield around it so its hard to see much but I do see the ground spring and it looks okay. I cannot find any evidence of any strap from the crt or shield to the chassis. Since this is a metal cabinet set it would appear that maybe it would just be grounded that way? I installed one of the chassis bolts with not change. (also tried a jumper wire from the shield to chassis) I then swapped the horizontal output tube (and reworked the tube cap, since it had some corrosion) plus the 3A3 and 6BK4. No changes. What I am getting is a real fireworks display in the neck of the crt and this worries me most of all. I hooked it up to the B&K tester and I have good emissions on red & blue but none on green. (odd that with the set running the green gun is active) I show no shorts in the intial test on the machine but when I flip it to clean/balance the heater light comes on. Doing this operation on the green gun made no real difference. I thought this might be a heater/cathode short so I cut the heater wires off the chassis & hooked it into a seperate 6.3vac power suppply. This changed nothing, I still get the light show. Sad, the crt seems so strong otherwise. Could something external be causing this arcing? It is intermittent, only pattern is it has to warm up for a minute. Tapping the neck has not helped, at least not for more than a second or two.

Here is a view of the neck while it was acting up. I would like to think this is not crt related but have no experience with this particular problem.

Bryan,
Just a thought that may be of a little help with your problem. Would you by chance have a test jig or know of someone who has a jig? You could fire up your chassis on a jig to see if the trouble is still there. If you no longer had the trouble with the chassis hooked to a test jig or CRT that would eliminate your set having a chassis problem. Good luck!

Jeff

i have seen that sort of neck glow when the focus voltage was missing.but a tube can test fine and still be gassy enough to do that.
try your b&k on another tube for a test.
i have had to repair socket 3 on my 467's due to broken wires.

Okay, here we go again. I have been working on this every other night-got to rest in between! I had pretty much decided I would have to swap out the crt but the last couple posts encouraged me to try some more. After more poking & prodding I realized I hadn't used the normal/service switch since the "fireworks" began. With the switch on "service" it was still acting up but there was no more arcing; the flat line would go dim/bright but would not dissappear. I pulled out the schematic, started tracing things out...took some voltage readings & at the screen & drive controls they were normal & unchanging; hmm...you know, nah, it couldn' t be...but just maybe...in trying to fix the color problem I had swapped the video output with a used tube that tested stronger than the old one. I recalled that I had not swapped it back. Folks, I didn't have time last night, but tonight I am going to take that old used Magnavox 12HG7 and I am going to smash it to smithereens so that it can never cause this trouble again:uzi:

Anyway, with the old tube back in the crt has not acted up the least little bit and I am back to the color problem. It is a little better now after some of the tweaking I have done. Right now when showing a scene Some colors show up and others won't, for instance the background may show up red, a woman's dress may show up blue, but faces, furniture, most other stuff is in pure black & white. Among other things I think I need to refresh my pile of 6GH8's. Its ashame that even a new tube can't be fully trusted.

6GH8's are and always will be noted (by me) as being the most unreliable trouble prone tube ever made. Definitly sounds like gh8 symptoms at this stage.

Back at it again with this set. What can I say...I must really enjoy working on these sets because if I didn't I'd have tossed this one out the door by now!

I ordered a fresh supply of 6GH8's, nice NOS GE tubes. Replaced them all. The tiny amount of color I could get did look a little better but not much. To refresh (and maybe correct) with the generator hooked up and the agc cranked nearly all the way I can get color bars, nice and bright; off the cable tv though I have to back off on agc and I lose what little color I have as I get it where its supposed to be. I did some more probing, and so began the next chapter. I had noticed that adjusting the burst phase coil had no effect earlier when I was measuring voltages. Now I saw that pin 6 of the burst amp, which is supposed to see 355v, was actually seeing just about nothing. (less than 1v) I found that the coil was reading open. Pulled it, could see where there had been an arc. My clumsy fingers just made things worse. Checked with Moyer's-what an amazing place! Had 'em in stock, they were here next day! I got 2 in case this one gets fried, too. So tonight I put in a new one, no change. Hmmm....now I see that the peaking coil between the burst phase & B+ was open. I no almost nothing about these; looked around and found what appears to be a good replacement, though it looks different. (color codes are same, ohms read right) Soldered it in, now I have TOO much voltage-405. I also have another problem, maybe related to the high B+-arcing. A few chapters ago I had something arc on the board and I wonder if that might have been what killed the coils. This today arced numerous times, though I had trouble getting a glimpse of where at. Finally, just as I was turning the set off there was a tremendous (well, pretty bad) arc right underneath the burst phase coil! I checked and it still reads okay. I can't find anything obviously shorted (no solder problems, etc) so once again, I'm just left:headscrat

Whaddya think, fellas? 50v too much couldn't be causing this, could it? And I wonder why its too high? Maybe I need a real match for the peaking coil? Any ideas? Oh, by the way, still no color:(

Too much plate voltage means the tube is not drawing current...check the screen grid voltage on the burst amplifier tube, also the cathode circuit.