Earlier in the year I worked on this CTC-31, finally giving up due to intermittent arcing in the area of the burst amp/color crystal. The last suggestion made here was to check for bad solder joints, especially the larger grounds. Well, restless, I pulled it back out Sunday & went to checking those joints. Nothing real bad, some sort of looked marginal so I fixed 'em up. The burst phase coil had previously gone open and I replaced it; I suspect this arcing took it out, and while I have a couple spares I don't want to kill one for nothing. There is a big ground trace beneath it so for good measure I ran an extra wire off it to the chassis. Everything looks to be in order. So I fired it up and as soon as the switch was turned on-LIGHT SHOW! :yikes: I narrowed this down to the area underneath and between the blanking amp & the video output. I pulled off the rear panel for a better view, and have not ran it for more than a second-hard to get a closer look. Once when I turned it on I got no spark, just smoke, smelled like wax, but I could not find anything hot. (no paper caps in this set) The next time I flipped it on, fireworks again. From seeing/hearing it, this is a pretty good voltage arcing. There are some things I can try (seeing what it will do with hv disabled, with normal/service switched to service, pullling tubes, etc.) but does anyone here have any good ideas? One thing I notice on this set that I don't recall running into before are spark gaps, lots of them, either alone or as part of disc caps, but I can't say thats related to anything here.

Is there any way you can operate the chassis with it out of the cabinet so you can see the bottom of the board where it's arcing? Does it arc before it's warmed up, or only after? Try disconnecting the CRT socekt. There aren't that many voltages in a TV that can arc unless the board has carbon tracking. Have you checked for arcing in the flyback?

I know the boost voltage in this set that is fed to the screen controls is more than 1,000 volts...maybe the arcing is somehow related to a PC board trace with this voltage?

FYI, the arcing occurs the instant power is turned on. Odd, I have a switched socket with (plugs into the wall, tv plugs into it, cord about 6' with a switch on the end) so I used that so I could kneel down & be looking straight at it when I flipped the switch. With cord switch off, I turned on the tv switch, it started arcing! But no AC? Or miswired cord? Light bulb plugged in same way didn't light! I want to ignore that odd problem for now! I'll rig up another such way to flip it on while I'm kneeling. It will scare the devil out of me when I turn it on, even though I know what is going to happen, but gotta do it! I don't see any signs of the arcing, though-no carbon or burnt spots. It will be a night or two before I can work on it again, think I'll try cleaning the traces good both top & bottom. There are spark gaps connected between the screen control shell & chassis ground, I suppose so that in the event of a short that shell doesn't go live with 800-1000 volts. I'll also see if I can get a look into the HV cage while this is going down.

Check the focus rectifier socket for carbon traces. Look for any tracks of carbon in the HV area. There are several spark gaps, unless the leads are bent and shorting they usually are not the problem. In other words you would only get a spark if there is a problem causing the voltage to go way higher than normal. There are gaps on c143, and c142 both in the 800volt boost. One of these is located near the screen controls, the other is under the HV cage. Also check the controls on the rear panel. The vert lin control has 800v boost on it, and can arc.
Good Luck

Bill R.

If it is arcing as soon as it is plugged in it has to be the primary b+ supply voltage arcing somewhere...could not be HV or not likely boost voltage as the horizontal output tube has not warmed up yet. You may want to disconnect the leads from the different branches of the B+ supply and see if you can pin down the arcing to a specific area.

I had a few minutes to work with this tonight. The chassis is on the bench, no connections to the crt or yoke, horiz. output tube removed.

I quickly switched the set on & off a few times with no adverse reaction. About the 4th time I got an arc, & repeated it. It was between 2 legs of the burst phase coil, the ground leg & the leg hooked to the plate of the 6GH8 burst amp. (355v per Sams) What was in between the two traces was, of course, carbon. I had noticed it was suspect here but thought I had cleaned the traces enough. This time I cleaned it with gojo & a toothbrush, then wiped down, then cleaned good with alcohol. Everything looks like new around there now. But I'm not ready to try it again. I know this was not the only place arcing, unless I was seeing things. There is a chicken & egg thing going on here-I assume it arced, taking out the coil at some point, leaving carbon, continuing the arcing, but I could swear other areas are arcing instead, on occasion. I have to figure out why. The plate lead also connects to a .82pf cap into the color oscillator and ACC circuits. This is where my lack of any 'real' training in electronics shows, as I can get to this point but have trouble grasping where the problem lies because I don't fully understand theory. This is how I learn, though. And I've learned more off these forums than anywhere else. Thanks for the advice so far, which I will continue to follow up on, & thanks for any advice to come!

Sometimes circuit boards break down for no apparent reason. The correct way to fix this is to physically scrape away all the blackened material with a knife. Cleaning it won't be a reliable fix.

I've worked just a little more on this. Got that trace cleaned up some more, and cleaned it out with a blade. Further testing shows no arcing, though I did get a slight wisp of smoke from an undetermined location on the chroma board with a waxy smell. This was with just flipping the switch on & off fairly rapidly. I don't know how safe on the chassis it is to bench test it like this-hv is disabled, of course, but this has got to put B+ too high, right?

Studying the schematic, I was eyeing the 80mfd filter cap on the 355v line. Could that cause problems like I'm having? I might have changed it out already but I don't have anything that high in value in stock (gotta place another order after Christmas) although I could parallel a 47 & 33.

(I might have played with it more but I decided I need to run each of the roundies for at least a short while, as several have not been running since early summer. Once I got the CTC-5 to straighten up and fly right I, of course, could not take my eyes off of it for the rest of the afternoon!)

Last night I changed the electrolytic cap in the last post. After giving things a once over I hooked everything back up, but left the horiz.output out of circuit. After a few seconds I noticed smoke, this time from R174 (see diagram), color killer emitter to ground. I hooked up the meter & tried again; Sams says to expect 2.6v here, but I got 115. I replaced this resistor (with a 1w) & also replaced or at least checked R173, R170, R177, R172. I replaced C131, a .82pf cap in the burst amp circuit, where I had problems earlier. (I was in no hurry to replace such a low value cap but I figure things are pretty screwed up anyway!) After all that I tried again; the new R174 is overheating & now reads 80v. Slowly, ever so slowly, I learn. Any ideas welcome-thanks!

BTW, if anyone is following along, this is Sams 987-2.

Shorted transistor q1?

I had my suspiciouns about Q1. (I'm suspicious of anything solid state!) Back in the spring when I was trying to fix the no color problem I substituted a NOS transistor here, though the old one tested fine. Tonight I put the old one back; no change. Also changed another off value resistor, this one between 2 of the filter caps. (Had gone from 680 to 1.2k) No change there, either.

What are the other voltage readings on q1? Of the resistors you checked or replaced, which ones were replaced? Did you check R176? It is part of the voltage divider that provides collector voltage to q1 from the Horizontal blanking amp. Is Q1 shorted?

In answer to Bill's question: C=113,B=114,E=102. These readings were taken with it on the bench, no hv, no yoke, etc. I also checked R176 & it was fine, much to my dismay! Am I smart enough to tell you without a doubt that Q1 is okay? No! Seems alright by my little Sencore tester; I bet those voltage readings mean something to someone smarter than me-I hope!

In answer to Bill's question: C=113,B=114,E=102

Usually transistors will have between their bases and emitters a
voltage difference of 0.7 (if silicon) or 0.2 (for geranimum). Unless
the transistor is biased off (passing no current). Where is that
color killer trimpot set? Looks like, depending on the setting, the
base voltage could be anywhere between 0 and 300V. Adjust the
trimpot so the base voltage is what the Sam's diagram says, and
then check to see if the other voltages around the transistor
are close to what Sam's says they should be.

Those voltages are all way high. It's late I will have to think about that one. I never ran one with no yoke and the HO tube out. Well I did run one once with out the yoke, but it burnt out a diode in the yoke circuit because there was no load. That was not a 31 though. I have a test jig to connect the chassis to, so it has the proper loads on the Horiz and vert. sections. The collector is connected to the grid of the blanking amp and to the grid of the horiz out tube through r143. It's late but it looks like you would have to have multiple componant failures to have the collector and base voltage so close. Like I said I will have to think about it some more. It will probably be something simple we are all overlooking. That's how my luck has been lately.

Okay, progress, for the most part. What I found was that the set was living up to it's nickname-still more arcing! Very light, across a trace, only visible when it was darker in the room. More 'scrape, scrape, scrape' and when I was done the voltages @ Q1 were normal! I don't know, something must have gotten on the traces or something odd because since then I have found 2 or 3 more that want to spark over! I ran it earlier today all hooked up (with hv) and it worked okay (no color) but shut it off when I tracked down an arc; later I ran it for an hour or so without any problems, then once again a real bad arc-over, in another location, this one was bad enough to kill the raster before I hit the switch. Out the chassis came again, more scraping & cleaning. If I can get beyond this I can tackle the color problem; with some adjustment I was getting some color, odd in that pure reds (like a red dress or lipstick) show up great but fleshtones and most other colors are very weak. Same basic problem I had before the shorts started. I'll be trying again soon, and if it holds without arcing I'll try aligning the colors.

So much for being on the right track. After carving out another arcing trace I put the chassis back for the 48th time, now sparks from yet another location! What is going on here!? This time I cleaned that new trace out, then also pulled open the hv cage to look for signs of trouble, but everything looked okay. When I again fired it up, more sparks, plus when the hv came up there was a hollow sound echoing, I couldn't see the screen from my position but I don't think there was a raster ecept for maybe a flash. I reseated the hv cage cover (this is the one with the 3A3 attached to the top cover upside down) in hopes that the connection was poor but no luck.

I am about to just put the back cover on and let it sit for awhile-maybe a long while! (it took several ordeals like this, with years of sitting in between, to figure out my CTC-5!) There are some other options:

A) Anyone wanna clean CTC-31 remote set, good project for ya?

B) Anyone gotta less finicky CTC-31 chassis gathering dust?

C) Anyone know whats going on with this thing?

Guys, I do appreciate the help you've given me.

I would say that either there's way too much voltage on the board, or the board has been contaminated with something that's causing it to break down under normal voltage. I would try thoroughly cleaning the board all over with alcohol. Arc over isn't a common problem with circuit boards. I've only seen a few cases in many hundreds of TVs and monitors I've worked on and they were always in one islated part of the board.

I tried to get a measure on the 355v line the last time I powered up but it was arcing too much so I had to shut it down. When it was behaving the bw picture and audio were great; seems like that would not be the case with a very high over-voltage? The arcing has occured only on the chroma board, but basically from one end to the other. I've swabbed much of it with rubbing alcohol, though I wondered if maybe that would leave something behind-I don't really think so, since the bad areas that creep up don't follow with where I have just cleaned. I can't see the flyback in action with this set, but could a bad one be introducing spikes that would cause this? Another strange thing, it never trips the breaker. Oh, well. I'm bringing home another roundie next weekend, my luck with them has been much better! (famous last words)

Try disconnecting leads from the B+ supply branches at the filter caps till you find one that stops the arcing. Remove h.output tube & damper so you don't overload it if the oscillator gets disconnected. Check the voltages at the caps once you disconnect the B+ lead that stops the arcing.

Also...
It sounds like you have an intermittant somewhere if you had a period with no arcing...maybe there is a ground connection to the circuitboard that has come loose? I had a condition of no horizontal oscillator in a CTC-38 that I tracked down to a loose solder joint on the B+ supply to the osc. Check the joints on the chroma board for microcracks, check them with an ohmmeter/continuity checker, resolder any suspect connections.

Well all the arcing would explain the odd voltages. You may have to find another set to get a replacement board. The color problem you indicated when it was working could point to the demodulator circuits which are also on that board.

I honestly had given up but the latest suggestions, especially Chad's idea to disconnect leads, made me pull it back out. And, what can I say: now it won't act up! One little spark when I tried it with hv and nothing else. I ran it an hour without problems and then last night I ran it from 8-midnight. Was it some loose or close wire that I moved away? (or component?) Or maybe just dumb luck? I'll keep my fingers crossed-I know chances are good it will come back. I tried pushing on the chroma board to see if it would act up, but I admit I didn't push very hard-I hate to look for trouble!

With the set acting right I set to work on the color problem. I did a quick setup )purity, basic convergence) & came up with a very nice bw picture. Tuning the station until the video was shot got me color but I couldn't get color on a decent pic. The IF coils had plenty of "screwdriver drift" to begin with so I stirred the pot even more. I did finally find a way to get a real, full color picture, though its not right: tune in a strong station just right, turn the agc a little too far into overload, adjust the coil in front of the 6KT6 (?memory?) and, voila, color, overloaded, but color. Well, I admit I'm in over my head when it comes to correctly aligning the IF. I can handle the ACC, etc., and right now all I've done is turn the coils until the color (when its there) stays put and is correct. It is encouraging to see that the set can produce a color pic if it wants to. Now if I can just make a color pic when I want it to! The bw pic when properly adjusted is very strong so I really think this baby could give a great color picture if I can work the bugs out.

(note: all 6GH8's are NOS GE tubes)

Does the no color problem re-occur when you turn the set back on after having adjusted it to produce color? May be a thermal condition...you may want to try the freeze spray on IF and chroma components. If it were an alignment problem only, once you aligned it to produce color it ought to stay that way.

One thing I have read is that low RF or IF gain on account of weak tubes can make color reception difficult. It says if you don't see snow and hear strong white noise with the antenna disconnected, you may have trouble getting color. How is the voltages at the IF and tuner stages?

How about your transistor stages on the chroma...have your voltages there returned to normal?