I've rescued an RCA CTC36XK console color television recently, and I've been working on getting it going again. It's a rectangular tube color set made in 1969. It has remote tuning with what looks to have been a high frequency sonic remote. (I don't have the hand control). The cabinet is in rough shape, but should clean up OK, and all the knobs are present and accounted for.

On first checkout, all the tubes are present, no nasty looking wires or anything that might catch fire, so I went ahead and brought up the power. All tube filimants light up, including the picture tube, but there is no deflection and no high voltage. There is also no sound. When the volume control is turned all the way up, I get a slight hum, and the hum changes a bit when changing channels, but no television sound or static. The UHF channel knob is frozen in place, and the light bulb for the VHF channel indicator is burned out. On closer inspection, I found that the VHF channel indicator reel is also not moving when the knob is turned. It's stuck on channel 13 (I wonder if that is a sign...).

Anyway, I went down to the main branch of the library, since they have all the Sam's Photofacts, and looked up the folder for this set, only to find out that some previous jerk had stolen the schematic page. I copied the rest of the information in the folder, included the schematic for the hand control. It looks simple enough to build one, provided I can figure out the value of that coil.

My inital instinct is to think that I've got a problem in the sets power supply. A lack of sound along with a lack of high voltage and deflection tells me that I'm missing a critical voltage. The electrolytics don't get warm, but one could still be open. A bad rectifier is also very likely. I pulled the chassis out of the set with a lot of difficulty, the tuner doesn't seem to disconnect easily from the chassis, so it had to come along. The tuner is very heavy and bulky since it has all the remote control motors and such. Under the chassis I found a large ceramic power resistor dangleing out by one lead! The other end looks like it had connected to a terminal strip that has burned and fallen apart, and it is dangleing from some burnt looking wire. I also found a rectifier that looks like it has fallen apart, as one lead can pull away from the disc part!

I'll post pictures when I get a chance, but does anyone have a schematic for this beast? This is the first color set I've worked on, so some of this is new territory.

Thanks!

-Ian

If you can find a ctc-39 schematic it will be very similar...ctc-39 is same as 38 with the addition of automatic tint control.
The device with the disc is likely the degaussing thermistor...it is in the 400 volt AC portion B+ rectifier circuit, directly after the power supply transformer. If it opens, which is common, you will have low or no B+. CAUTION: there is 420 volts DC with a lot of current capabilites at the B+ supply.

If there is a burned resistor, you likely had a short in a filter cap and this caused the resistor to burn...have seen this many times on these sets. Would recommend replacing all those power supply filter caps or at least the one that the burned resistor connects to. Also shorted diodes in the power supply are common. Use a 60-w lightbulb in series with the powerline when you make the power supply repairs to serve as a short indicator (if bulb lights bright and stays bright...there is a short still). This will prevent further damage and help diagnose where the short is if still present.

Also...the normal heat from resistors often causes burned wiring and terminal strips in these sets...you'll just need to replace the wires and install a new terminal strip.

Yes the tuner is kind of difficult...it has to come out with the chassis, there is no plug arrangement. What I have done is to remove the chassis bottom screws and leave the chassis hooked up in the cabinet and insert something like a book or video tape to prop up the back of the chassis so I can make test connections. I'll use alligator clip leads to hook up the voltmeter, not putting my hands under the chassis while it's plugged in, in case it were to fall.

iirc the tuner comes out and hangs on the chassis.
look for a tuner service mounting.

yup... those RCA chassis are the easiest to remove. You take all the knobs off the front, loosten 4 screws, and you lift up and pull out. I had to pull out a TON of CTC-38 chassis back in the shop days. The CTC-38 /39 chassis were one of the last tube chassis (for consoles anyway) RCA really went on the cheap in those sets. I loved the design of the cabinets they used, but hated that chassis.

Chad pretty much said it all there. Those ceramic wire wound resistors would commonly burn up/open resulting in a loss of B+. Those same resistors got hot enough to really burn up other close components expecially wires and the termial strips they were soldered on.

The stuck UHF tuner is common in almost every RCA set I came across. Problem is dried up grease in the UHF gear shaft. the steel shaft is inserted through about a 1" bushing on a pot metal bracket. the grease will dry up, turn into a gummy substance. Do not attempt to try to break it loose with pliers by turning the shaft or gear. What works best is to use a hair dryer or heat gun (yes, another heat gun trick for TV repair!) and heat the bushing. Be sure to pull the E clip off the end of the shaft so you can remove it. Once you get it hot enough, you can turn the shaft with a gentle twisting motion and pull it out of the bushing. then use a cotton swab of WD-40 or some other petroleum lubricant to break down the grease inside the bushing and on the shaft. Reassemble using any kind of oil, it will work as good as new.

Do you have a model number available? Keep an eye on ebay for remotes. Those rca 7 button ultrasonic remotes appear every so often.

If you can't find the sams I should have it and could mail it to you. If you need it send me a PM with your address.

Well, I did some work on the set today. I called a local electronic parts store and asked for the thermistor. The guy knew exactly what I was talking to when I asked for a thermistor rated for 120 ohms when cold, and that it was for a television set. He asked me what sort of a set it was for, and when I said that I needed it for a 1969 RCA console, he actually knew precisely the part I needed. He even knew the original RCA part number. Apparently they haven't had anything like that for a long time, but he said that he had a modern RCA replacement that he said should be a usable substitute. So, I went down and picked up the part. May not be exact, but it should work.

I patched up the burned wiring under the chassis, and reconnected the power resistor. It doesn't look like the resistor was damaged, and it still measured the proper value. I also replaced the thermistor with the new substitute.

I plugged the set into my homemade dim bulb tester with a 60 watt light bulb in it. Turn the volume knob a tiny bit, and the indicator on the front of the set lit up, but nothing else. Turn it a little bit more, and the light bulb on the dim bulb tester lit brightly, and the indicator on the front of the set went off. So... I still have a short in there somewhere. I don't dare bypass the bulb in the tester with something like that. I need to do some more thorough investigating. Something tells me that I have a shorted electrolytic (or two). The power resistor that burned off the terminal strip is a 560 ohm unit, and located underneath the chassis, near the shunt regulator tube, with one leg connected to a small transformer under the chassis. Not sure at the moment what part of the circuit that this resistor is part of at the moment, I need to do some more investigating, but that means hauling the chassis back out of the cabinet again.

I was really hoping that I could get away with something simple here, but no such luck. I guess when this television was sitting there awaiting it's destruction, it looked at me like "I can work, honest, take me home, fix me..." Oh well, so - the simple quick fix didn't help this time. I need to pull out the chassis, and really clean out the crud, and sit down and work through the circuit, checking parts. Not to mention repairing the wiring that's managed to break free from the tuner in the process of moving it so much. When I first started, there was a random loose wire that was hanging free from the tuner's relay board. Now I've got another, as well as the cables for some of the knobs on the front of the set that have broken free. It looks like this set's been serviced a bit in the past, and the wiring is getting pretty brittle. I also need to disconnect the electrolytics, check for shorts, and replace what I can. Problem is, this set employs many electrolytics, three of which are large multi-unit cans. Ugh. This is going to get expensive. I just hope the picture tube is good.

-Ian

Ian, Have you also checked the flyback to make sure it is good? I would check that before doing any further work. Check the flyback and make sure there are no burn holes and also smell inside the can to make sure there is no burnt odor. I know I probably sound like a broken record on these posts, but flybacks were RCA's main weak point and usually the main cause of failure on those chassis. I'm only stating this because there isn't much point in doing all the other work if that isn't attended to first. As for the picture tube.... It probably has a 25XP22 which was a pretty durable tube. I wish you luck on the repairs, and you've got a pretty "high-end" set for it's time if you have remote!

Yes...the flyback is a possible problem on these sets, but it seems like the flybacks got better by the time RCA got to these sets...have not noticed as many cases of flyback failure on the 38's/39's as on the CTC-31's and CTC-16's.

To diagnose where the short is, I start at the end of the filter capacitor/resistor chain, farthest away from the rectifiers, and disconnect one branch at a time, and then observe the short checker lamp to see if a short is still present. If so, I continue disconnecting further back the chain till the lamp goes dim. If you get all the way back to the diodes and the lamp is still bright, its likely shorted diodes.

Hey Ian, How is the set coming along? Found this remote unit on eBay which is probably for this set. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3638&item=6158147039&rd=1

Ugh. This is going to get expensive. I just hope the picture tube is good.

-Ian

If you like, I can send you my B&K picture tube tester to use. We're not that far away from each other, so it wouldn't take long to get there.

Well, I had a little bit of time this weekend, and I pulled the chassis out of the console, and dragged it down to the workshop. I haven't really done much in the way of troubleshooting here, since I didn't have much time to work, but I've cleaned it a bit, and looked around, getting myself familliar with it's layout. This is by far a much more complicated chassis than any of my previous projects, I've worked on several black and white sets, mostly Zenith - with their beautiful metal chassis/hand wired design. This set has printed boards, and many bundles of wire. Of course, this is also the first tube color set I've worked on...

OK, so, I measured the resistance between the hot and neutral on the power input when the switch was set to ON. Less than 1 ohm - not good. It didn't do this before I fixed the wiring, when the power resistor was disconnected, underneath the chassis when I first found it. All the tubes lit up before. This is good, since that means that my power transformer has a good chance of being OK. Also, the flyback looks to be in good condition, physically anyway - it's not burnt or cracked, and it's not even too dirty, since it's inside that nice little metal cage. The offending resistor - the one that had been disconnected at a burnt terminal strip is connected to what appears to be some sort of choke or transformer, which is connected to the shunt regulator tube, a 6EN4. Removing the tube does not clear the short, so I've likely got something electrolytic that's shorted. Attempts to trace the wires from the shunt regulator back to the power supply were unsuccessful, the wires are tightly bunched together, and some have faded a bit, making identification difficult.

I don't have a schematic for this set, since some <explicative deleted> stole it out of the public library. This is a CTC38XK, Sams #1092-3. Looking up on Sams website, I see that there is also a Sams #1000-3, which covers the CTC38X, XAD, XAE, XP, XR, XT, and XU. What's the difference here - is it anything major, or are they mostly the same? I know someone suggested getting a CTC39 schematic, since that's close too, but it would be nice to get as close as possible.

I obviously need an electrolytic or three, but in order to save a little money here, I'd like to start by replacing only the shorted one, and see if I can save the rest. This set uses several 450V electrolytics, and I can't seem to find appropriate replacements for them at Jameco, and even AES has a very limited selection of higher voltage caps. The caps in this set are very cramped in there, however, getting them out to replace is going to be fun, so I may just go ahead and replace a whole can at once. But, regardless, I do like to figure out _what_ failed before replacing piles of parts. That's part of the fun. I'm going to stop by the library after work and see if I can get the schematic from 1000-3. At least then I'll have a starting point.

It's times like these when I wish that the day was like 36 hours long. Either that or I didn't have to work. Or both. Stupid reality getting in the way of my repairing televisions... Hopefully I'll have time tonight to actually fire up the soldering iron and get some actual troubleshooting done, instead of just staring at the thing :)

-Ian

Were you the guy that was able to make a copy of the SAMS for the CTC-38 with the exception of the schematic? I have scanned the schematic for the CTC-38 from a TekFax. They were schematics that were include the monthly Electronic Technician Magazine. Email me if you are interested.

Ross

[email protected]

Ian and All,

I scanned the schematic in 4 PSD Adobe Files.

Ross