A few weeks ago, the high voltage on my CTC-53 started going intermittent shortly after I switched on the TV. The raster would collapse and 'diffuse' into weird color patterns as the HV flashed off and on; I let it run long enough to verify it was a physical/vibration-related intermittent (tapping the side of the cabinet would make it go on/off fairly consistently), but I switched off the set pretty quickly.

Anyway, this is one of those many RCA color TVs where the HV rectifier top cap is pressed directly into a receptacle on the flyback itself, rather than connected with a wire lead. My first guess was to check for a bad connection between the HV rect and the flyback. There was a little carbon in the flyback contact, so I cleaned that out a bit. There's a short metal coil spring in there that I assume helps preserve the contact between the HV rect and the flyback, so I wiped that clean too and spread it out a bit just for good measure. Cleaning the contacts removed most of this translucent paste 'goop' that was covering the contacts (some sort of oxidation preventor or arc preventative or something..?), but I tried to leave as much of that as I could. I pressed on the HV rect panel while bolting it in place to try to make sure it was in nice and firmly. I switched on the set, and everything was fine. I left it on for a while to make sure it got fully warmed up, and it worked flawlessly the whole time, so I figured that was that.

The other day, though, the HV quit again briefly for a second or two, but it came back and was OK after that (I let it continue running for several minutes while watching carefully for further signs of HV failure, but then shut it off though nothing more had happened). So, perhaps the contact is still a bit flakey. Is there some 'trick' to this style of RCA flybacks? Is there something important about that 'goop' that was on the HV contact-- should I re-dress the contact with new 'goop'? What is that stuff anyway?

if that is a 18 or 19 inch portable. here is your trouble. on the board above the horizontal output i know it has a 5gh8a or a 6gh8a on it. i believe there is also the vertical out tube on the board. around the socket of the 6gh8a there is about 4 or so resistors that is changing value they are up next to the tube socket i believe. but it has been a long time since i have seen one of these. the symptoms you are describing are the exact same as when those resistors change value. it will get to the point of flashing all the time. wish i could tell you the resistor numbers . maby someone here can. steve

I have never had trouble with flybacks on the CTC-53 type chassis, (unlike on the other types such as the CTC-31 etc. that use a similar flyback connector).
If there was a bad connection at the flyback you should hear sizzling/arcing.
I was having trouble with improper screen voltage at the horizontal output tube causing a lack of HV but cannot remember exactly what I did to fix it.
It was a resistor related problem like what RCAMan is talking about.
Monitoring screen/suppresor/grid voltages at the horiz output tube should help narrow down the trouble source.

Thanks for the input, guys!

At first, it looked like RCAman may have hit the nail square on the head-- as he says, there are four resistors right around the 6GH8A horiz osc tube, and one was indeed a tad out of tolerance (R40 measured at 268k instead of 220k). The other 3 were right-on though, and one of those in fact had obviously been replaced at some point in the past.

Replaced R40, switched on the set, and all was OK..! ...for about 10 minutes, and then the HV started flashing on and off again. :(
BTW, Chad is right that there is no arcing or ozone smell when it cuts out. You can hear the horiz oscillator whine drop and start buzzing, though.

Anyway, since the back was still off, I left the set running and I started tapping poking around with an insulated screwdriver, hoping to joggle the intermittent, but couldn't find it. Several blasts of component cooler spray didn't catch it either. Then I spotted an odd charred-looking spot on C5 (mylar .082uF 600V) in the damper circuit. Tapping the cap near that spot *seemed* to speed up the intermittent, but couldn't be sure. Switched off the set, waited for it to cool down, replaced C5.

I'm not so sure that fixed it though. After switching it on, but still during the "warm up" period, (the CTC-53-and-friends take a loooong time to warm up to the point of producing a picture) I heard the tell-tale horizontal osc 'buzz' for a few seconds, but there wouldn't have been a raster yet anyway. The raster appeared and all worked fine after its normal warm-up time, but I'm still kinda doubtful it's actually fixed-- I guess I'll have to see if it starts cutting out again while it's actually "warmed up". I'm done looking at it for tonight though; I'll come back again to it later...

I think heat may have been a problem on these sets. I have one that had vertical problems. I ended up replacing all the orange drops on the vertical board before I could get it to work fairly decent. Still not perfect. All those caps & resistors are right in the path of all that heat drifting upwards. And yes, these are s-l-o-w to warm up. I think I timed mine at like 42 seconds to produce a picture.

Knock on wood (*knock* *knock*), but I think I might have it fixed now. :)

This afternoon, I switched on the set and right from the get-go, the HV just flashed and flashed non-stop. So, I put it on the "bench," pulled the back off, switched it on again, and wouldn't you know-- it ran perfectly. I must have let it run for an hour, and it still ran great. Tapping the cabinet, the chassis, and various parts didn't have any effect at all. Switched it off, came back a few minutes later, switched it back on again, and now it's in disco mode, flashing on and off like mad. Nothing seemed to consistently get the intermittent to start or stop. Tried switching it off, waiting several minutes, switching it back on-- sometimes (one time anyway) it was well-behaved, sometimes it ran a moment, flashed a few times, then worked great again, and sometimes the HV just cut off and on constantly.

Well, lacking any better/easier ideas at the time, I figured, eh, how about just trying a new 6GH8A horiz osc tube and see what happens (I knew I had a couple of spare 6GH8A's around). And wouldn't you know, but it looks like that was it after all. After swapping that tube, it's been running great, even after a few restarts and letting it run for 10-20 minutes. I guess that tube had just developed some sort of weird intermittent; even tapping the tube and wiggling it in its socket wouldn't trigger it, but I guess ya never know..!

Funny how it turned out to be such a simple fix though-- I shoulda thought to try that earlier..! ...chee...

BTW, bgadow, when I first got this set a few years ago, it had a case of bad vertical linearity, and it too needed a new mylar cap in the vertical osc circuit to make it run right.

those resistors i was speaking of. i would change all of them. always cured the ones i worked on. steve