Need some advice (help) with my CTC-16L

[jstout66]

I need some advice on what to look for concerning an annoying intermiitant problem. This is on the CTC-16L I got off eBay a few weeks ago. When I got the set, the picture was pretty good, but you had to adjust the controls more than usual when you turned it on. I suspected some bad tubes and found some assorted ones with shorts. What I changed (and I did check the new ones) was the 12BY7 both 6GM6's both 6GH8's 1 6HZ6 and the 6KZ8. Now every once in awhile the picture will flash green and go back to normal. I noticed the kine bias switch was a tad touchy (and would cause the set to flash if I moved it) and I cleaned it. The set still does it. I suspect from troubleshooting in the past that it may be the 12BY7 or maybe even the 6GU7's altho they test good. I was a dumbass and threw away the old tubes. The set didn't do this until I changed them. What do you think I'm looking at? I was careful with removing the tubes and all connections seem tight. I don't think the picture tube has a short, but won't rule that out. I'm mainly leaning towards the tubes I changed. What do you guys think?

[Big Dave]

This will sound strange, since I had a similar problem with the blue being over dominant. Check all connections on the CRT socket there the leads connect to the chroma board. I found the solid blue barely making contact. It popped right off and I clip leaded it. Problem solved. Also, check all solder joints on the tube sockets, especially the 6GU7's. I ended up hardwiring some of the connections to the replacement tube socket (one of the 6GU7 sockets was so loose, replacement was the only option). Now, if I could get the convergence worth a damn...

[RetroHacker]

I assume you've checked the obvious, like cleaning the tube pins, wiggleing all the tubes, etc... If this was a solid state set, I'd suspect bad solder connections on the board, but since this is a tube set, it shouldn't suffer from thousands of bad solder joints. But, if this set has been serviced a LOT like you mentioned, I'd check tube sockets for damage, wear, or cracked solder joints underneath the chassis, and make sure that none of the sockets have cracks in the bakelite/plastic/phenolic/whatever or show signs of arcing. Also, it could still be a bad tube - even if a tube tests good, it might not work great in a specific circuit - same with weak tubes. Some tubes may test weak, but work perfectly in a givin circuit, i.e. a weak 12AX7 will work perfectly as a phase inverter tube, even though it might not work as a preamp tube.

Also, try gently tapping on things with a plastic pen or something while the set is running, put a big mirror in front of it so you can just look around and see the picture in the mirror. Tap on controls, tube sockets, connections, etc - it could be another dirty pot in there somewhere.

I've had stuff with intermittent, nagging problems before - sometimes it's just best to sleep on it, and come back the next day, or have someone else come over and look at it, sometimes a fresh pair of eyes can help.

If problems persist, you might need to take on more drastic measures, possibly involving goat's blood and candles.

Good luck!

-Ian

[jstout66]

heh! I hear ya and I will check. I can hear my Uncle (the repairman) telling me from the grave "SEE! you should have left well enough alone" He used to get ticked because when a set came into the shop, and it had alot of use, me or my Grandpa would check EVERY tube and replace the bad ones. He always would fix the specific problem and tell us that by doing what we were doing, that it may cause more problems the set didn't have to begin with. Guess I didn't learn. This set has a TON of use on it, but the boards don't seem brittle. If the set was this glitchy no wonder the people kept a service contract on it for years. This is the set I bought of eBay for $310.00 that I discovered had the picture tube changed with a brand new one in 1977 under the service contract. I don't think the sellers I got it from had it on much. I shouldn't expect so much out of a 41 year old tv, but still....... Also my convergence is a tad off but I'm not even going to mess with that! I'll see if I can con a tech in the area to do it!

[Charlie]

I would suspect the 6GU7's as well. I recently swapped out a 12BY7 because of one problem, and come to find out, the new tube gave me a new problem. After suspecting everything other than the new tube (and replacing many parts that really didn't need it), I went back and plugged in a used 12by7 from my "pulls grab bag" and the used tube worked perfectly! Believe me, after all those hours of looking at other possibilities, I was quite annoyed to find the new tube was just as bad as the old one.

I was also getting the green screen on my 15... turned out to be a 6GU7 that was having trouble making good contact in the socket.

[jstout66]

I have an update. The set STILL has the problem and I noticed something else. when it flashes green for a moment, the set's picture will also flicker for a bit with retrace lines on top of the screen. You never know when it will do it, but it seems it's after the set is on for a half-hour or so. I tapped tubes, and sockets, and it doesn't seem to fix it, or cause it to happen when working. All tubes test good. What circuit or tube should I be looking at ? With my skill level, I HATE intermittent problems.

[roundscreen]

Jstout. you may want to check for burned wires on the color board. look for them behind the 6Gu7s. Also go after the grounds.

[Chad Hauris]

I have read about bad connections to the ground side of the filament on the 6GU7's causing the tube to shut off...also heard some reports of CRT damage due to excessive beam current somehow when the 6GU7 quits.

[kc8adu]

swap the 6gu7's and see if the problem moves to the red or blue.
iirc red/blue are in one and green/blanking in the other.

[Charlie]

On my 15, the 6GU7 on the right corner of the board closest to the HO tube was the issue. It was causing the entire pixture to go green. In order to make the color straighten out, I had to move that tube around ALOT. It wasn't just a matter of tapping it or rockin it back and forth. And, I could only find this one tiny little position for it to be in and work. Once I got it there, all was good. Finding it was the hard part. Kinda like a boy getting his first piece of... um... well you all know what i mean. Some of ya'll might even still remember!

Any of the wires that run across the top of the board... check to make sure they look healthy near the solder point. My same 15 had a wire to run heaters across the top of that board... was a little corroded at one end. Come to find out, it was a lot broke, too! I kinda doubt your problem is a heater connection, but, some of those wires might be for something other than heaters.

As far as other components, you might try taking a pencil eraser and start on the chroma board... push lightly on each capacitor, resister, coil, etc. I found a cracked coil on a color board in my Curtis Mathes that way that caused an occasional loss of blue. When I pushed it one way, blue came in. Mashed it the other way and blue went bye-bye.

[reeferman]

Take your 1/4" nutdriver (aka #8 in the old days), and give the neck of the crt a good tap tap tap and see what happens. It works best when picture is acting up. Most likely it isn't the crt in this case, but one never knows.

[jstout66]

I hope it isn't the CRT! It was such a bonus to have a Colorama tube in this set from 1977. No halo or delamination either. I will try it the next time it acts up. This might sound like a dumb question, but would a 6EW6 (Burst Amp) cause any of these problems? I re-tested all of the tubes and now I see my 6EW6 is bad. (many shorts) and it wasn't before. I did get another pair of 6GU7's. While it didn't cure the problem, it is less frequent. Now I'm wondering about this 6EW6.

[reeferman]

Burst tube will not cause this problem.

[rcaman]

i had the same problem. i put in 2 new 6gu7 ge tubes in my silvertone roundie.
i would flash green . resoldered everything. changed out the new tubes and the problem was gone forever. the new tubes checked good.

[jstout66]

well... I have another question. I'm taking out the chassis for repair, and I can't get the damn picture tube socket off. It's like it is frozen on. I don't want to damage the tube by forcing it too hard. Is there a trick to loosen it up?