CTC140 (RCA Dimensia) Rapid on/off & No Sound

[olePigeon]

Hello. I have a nice RCA Dimensia console television with a CTC140 chassis. I picked this beauty up free off Craigslist about 6 or 7 years ago. It had a few reoccurring issues that I was unable to diagnose and fix since the day I got it, but unfortunately it's now progressed to rapidly turning on/off. I'm afraid to leave it on in this condition to try to diagnose it for fear of damaging it further. These were the original issues:

1. When you first power it on, the sound would pop and hiss on the right channel only. After the TV warmed up, the popping would go away, but there's no audio on the right channel (this may or may not be related to the main issue.)

2. The main issue is that the CRT would randomly shut off for a brief moment, then come back up. On rare occasions the color would be distorted. Turning on/off the set fixed it.

Well, it had its last fritz, and now it's rapidly turning on/off. I can not find a schematic that isn't behind a paywall and only have the two service documents from inside the set.

I did find 4 1uf 50v capacitors that were all completely dead. I replaced those and tested the rest, but they were surprising all good. I had a brief moment of joy cuz the TV set cam back up when I plugged it back in, but zero audio. There was a light popping sound coming from somewhere, but I couldn't find it. Then a day later when I was going to sit down to troubleshoot the audio, the tube had reverted back to rapid on/off. I'm hoping the flyback isn't bad, although if I could definitively know it was the flyback, then I have no problems replacing it. Looks like a replacement flyback is only $20.

I tested the Horizontal transistor with my cheap component tester it tests good (although I don't know if it'd know if it was leaking or not.) I have yet to test the resistor near the transistor that can short and go bad, so I really need to do that. Cuz if that's shorted, then it's likely the transistor is going as well.

My deep dive in Google searching for (and failing to find) the schematic seems to indicate the most common point of failure are the diodes. I've tested all of the relevant diodes, and they test fine with my cheap tester. I would be OK with just shotgun replacing all the diodes anyway, but without the schematic with the parts list, I don't know the ratings for any of them.

Could use any help. Thanks.

[olePigeon]

While I was waiting for any help that my come by, I reflowed the solder on the power transformer and flyback transformer. When I went to test a resistor that connects to the Horizontal transistor, the pad completely lifted up. It was barely holding on. The area was also super dark from a lot of heat. Resistor tested fine, so I added fresh solder and ran a heavy duty jumper wire.

Picture came back up and has turned on every day this week in the morning and evening. So I hope maybe it was just a cracked solder joint somewhere (or that lifted pad from the resistor.) Who knows. The popping sound I used to hear is no longer there, so that's good.

Audio still doesn't work, but I can tackle that next.

I could still use a copy of the schematic if anyone has it so I can check voltages to the ICs.

Thanks.

[Electronic M]

I don't touch sets made after 1980 nor do I keep service literature that new... But I do know you buy the service literature from this source: https://samswebsite.com/en/photofact...earch&s=Search may want to search the model number to make sure you have the literature for right version of the 140.

[damen]

Your on-off problem was most likely solder issues around the transformers. The diode connections off of the power transformer were usually the cause, very common issue back in the day.

[olePigeon]

Originally Posted by damen

Your on-off problem was most likely solder issues around the transformers. The diode connections off of the power transformer were usually the cause, very common issue back in the day.

Yeah, the SIP board was the first thing I checked. Diodes check out and I added new solder and removed the old glue. Unfortunately, after using my TV over the long weekend, it began turning off & on again. I guess it's still possible one or more of the diodes is going bad even though it tests OK out-of-circuit.

On one of the occasions when it shut off and came back up, the colors were all messed up. I'm going to check the components around the degauss circuit. Maybe the power is fine but the degauss is triggering when it shouldn't. I do hear what sounds like a relay that will click when the tube fully turns on, although I don't know where (or if there even is one) the relay is located to test it.

[olePigeon]

Originally Posted by Electronic M

I don't touch sets made after 1980 nor do I keep service literature that new... But I do know you buy the service literature from this source: https://samswebsite.com/en/photofact...earch&s=Search may want to search the model number to make sure you have the literature for right version of the 140.

Thank you for the resource, but I'm not ready yet to spend $35 on a copy of a schematic.

[damen]

I'm trying to post a reply, but this stupid site keeps telling me I'm not logged in !

[vol.2]

Originally Posted by olePigeon

Thank you for the resource, but I'm not ready yet to spend $35 on a copy of a schematic.

I mean, that's the price of a McDonald's lunch for 2 now...

And also you can pay less for the digital download. I pretty much always get one if I'm working on a set. The amount of time and BS it saves me is far more valuable than the cost of it

[Electronic M]

There's a chance if you go on the world radio history website and comb throughout enough ETD magazine scans of issues from the era of this chassis you might find a free schematic. Whether you want to hunt that snipe to save a buck is your call.
Another thing to try is looking up the Sam's number ####-# on eBay and the like to see if you can find an original paper copy for $5.

If you plan on working on a lot of TVs it's advisable to keep an eye out for a bulk sale/giveaway of a TV shopps Sam's library. Sometimes they can be had for free. I've got around 1800 Sam's sets from the beginning until about the end of 1979 as a service library.

[olePigeon]

Originally Posted by Electronic M

Another thing to try is looking up the Sam's number ####-# on eBay and the like to see if you can find an original paper copy for $5.

Thanks for the heads up. Grabbed a SAMS for $10. Had the RCA CTC-140B and a Panasonic bundled together. I don't plan on servicing a lot of TVs, I just want to get this one working. I'd rather have a legit service manual than paying someone $35 so they can continue to gatekeep public domain stuff behind a paywall.

I'll scan and upload if anyone is interested.

Looks like it's 130V input voltage max. Not sure why I was fretting over this, I could've just bought a few 1000V diodes and be done with it.

Anyway, got the service manual. Ordered one of those diode kits with like 250 different kinds and ratings. Cheaper than buying off Digikey right now when you include shipping and potential tariffs. The symptoms for my TV are what you'd expect if that SIP board was misbehaving, so crossing my fingers that replacing the diodes will be a quick fix.

Fallback is that I'll have the schematic. I think there's enough room in the cabinet for me to flip the chassis upside down and have it all hooked up so I can further diagnose it if needs be.

[olePigeon]

Replaced the diodes, no change in behavior. Shoot.

[mgross0]

I had one of those things. Would turn on by itself in the middle of the night at FULL volume. Sometimes it would turn itself off. It was just a shorted relay, easy fix.

[wb2mep]

Resolder the pins on the horizontal drive transformer. Small transformer connected to the base of the horiz. output transistor. I had a 1992 vintage RCA start the same on-off cycling while troubleshooting another problem, and that was the cause.

[olePigeon]

Some updates, but please bear with me, I know next to nothing and am doing my best.

I replaced the diodes with "universal" diodes on the subpower board that tends to be the issue with most sets, but alas, not mine. The TV worked sans-audio for a few hours. The next day, kaput.

However, this time it was no raster or anything. Which I think might be a blessing in disguise because I can at least just follow the voltage, right? Hopefully.

I finally got the chassis mounted in a vertical position so I had access to the backside of the components while everything is connected.

I tested Q4900 which is the auto-shutdown transistor, and it was under at 9.7v. Schematic said if it's over 10v, that will put it in auto-shutdown mode.

So I followed the voltage to T4100, the "VIPUR" transformer (the one before the flyback.) I see the voltage coming in (although both 150v and 130v read as 88.8v when the set is on, then spike to their expected values when I turn off before falling down to zero.) However, on the other side of the transformer is nothing. Zilch. Zippo. And by extension, nothing is getting to the flyback.

I tested continuity on the transformer in-circuit on the "good" side. It has continuity, but resistance. When I test it on the "bad" side, it is OL with continuity.

I think the transformer is bad? What do you guys think? I'm going to desolder it from the board and test it again with the multimeter.

[olePigeon]

Originally Posted by wb2mep

Resolder the pins on the horizontal drive transformer. Small transformer connected to the base of the horiz. output transistor. I had a 1992 vintage RCA start the same on-off cycling while troubleshooting another problem, and that was the cause.

I will check that one, too, thank you.

Edit: Duh, there's no voltage to the horizontal transformer cuz there's nothing coming out of VIPUR.