CTC 21 goin green

[RCAkid]

I have a CTC-21 that I am about to begin the restoration process on. The good news is that I have a pretty clear picture so we have IF, HV, Audio, some color sync and virtually every circuit is working.

Now, in trying to establish what all is going on with the chassis, I am currently unable to attain a red raster/screen. After checking purity, the best I can accomplish is a reddish/brown sepia tone picture when the red screen control is full on and the blue & green are turned all the way down. I have had this CRT/yoke combination working and converged properly and tested with at CTC-38 chassis. So I know the purity and yoke are working properly.

Green seems to be the dominate color and until the set warms up, green overrides even the blue. Amazingly I can attain a near b/w picture but only if the red screen control is on full, the green down all the way and the blue added in a bit.

At this point, I can get some color sync, blues, yellows, greens but no red for facial tones. By adjusting the tint control, flesh tones are either green or blue.

Now knowing how squirrely 6gh8a tubes are, I replaced the two on the chroma board with known good replacements. No change. I changed the
6jc6 as well with no change.

Basically, I am really missing red. I have not re-soldered the pc board chassis grounds yet and that may well be the problem. I know that is a must do for all pc boards in this type of chassis.

I also suspect that the caps in the power supply are weak or there are resistors that are off as when I turn the green screen control to max or turn the brightness control to max, the picture goes out of focus and shrinks a bit horizontally.

Also, there seems to be some vertical issues. While there is no rollover and the screen is filled out properly, it annoyingly expands vertcally, just a little bit and shrinks just a little bit rapidly almost as if someone were playing with the linearity controls just a tiny bit. The screen has full raster/picture while this is occurring. I do notice some of the shields on the IF tubes are missing and I will have to find replacements.

So, with all that said, any thoughts on where on the chroma board and what components I need to be looking at to correct this problem?

I have a similar issue with at CTC-16 but I am able to get a red raster. Just green tries to be the dominant color, especially when there is no signal (green snow instead of white snow). Any thoughts on this issue would be appreciated too.

I know this is a long thread but I figure the more info I can post, the better the educated guessing.

I realize this is a complicated chassis and this is my first color set restoration. Since I grew up with this set, I figure it is the best one to restore first as I know this chassis best.

Thanks to all for your help.

[RCAkid]

One thing I just noticed, on the video/chroma board, the schematic calls for a 6KE8 for the color killer/chroma bandpass amp. What is on the board is a 6GH8A. I don't recall the 6GH8A being a sub for the 6KE8.

Any verification on that one?

[Chad Hauris]

I would set the service switch to service and see if a red line can be achieved.
Check the grid and screen voltages at the CRT for each color and see how they compare (danger: there can be 800-900 volts at the screen leads, make sure the meter is rated for this)

Most times though I have seen this problem it's been weak CRT's...seems like red gets weak first.

[RCAkid]

Chad,

Ordinarily I would tend to agree with you on the CRT. However, this crt is a reman tube with roughly 20 or so hours on it. Additionally, the emissions are solid on all three guns.

Even besides all that, I had talked about putting a CTC-38 chassis on the tube/yoke and trying it out in my previous thread. When I had the CTC-38 attached to the crt, the color was perfect as was red raster. I stuck the CTC-38 in the cabinet just to verify the yoke, convergence and crt were working correctly.

So I know the problem is in the CTC-21 chassis at this point.

But certainly checking the voltages is one of the first places to begin and I appreciate your help.

I was kinda hoping to save some uneccessary troubleshooting if some of the much more experienced techs out there had any short cut solutions or recalled any trouble spots that I should go for first. It would be nice to know all the circuits are working properly prior to recapping.

[rcaman]

your verticle problem as described to me. sounds like a leaky main filter capacitor. is the picture breathing or have a slow hum bar rolling up the screen. you may have low b+ voltages throwing off the other circuits. feel of the electrolytics and see if they are unusally warm. steve

[radotvguy]

I aint no expert on old tvs , i pretty much dabble with them , however i had a rca with similar issues and i recapped the electrolytic caps and checked all solder connections , resoldered chassis grounds and replaced the video output tube as well as the color tubes and adjusted all colors , then it seemed to bring the set back to working order .

[RCAkid]

rcaman: your verticle problem as described to me. sounds like a leaky main filter capacitor. is the picture breathing or have a slow hum bar rolling up the screen. you may have low b+ voltages throwing off the other circuits. feel of the electrolytics and see if they are unusally warm. steve

I have never heard a vertical problem described so perfectly. Yes, the screen seems to be "breathing."

Well, as usual, the first place to begin is recapping the power supply. I am very grateful that the set is working as well as it is. It demonstrates no real major problems.

I suspect as well, that after recapping, the power supply should return to its robust self and the picture squash/out of focus when the brightness is turned up should be resolved as well.

Besides the solder joints on the pc boards and making sure the voltages are not overloading the flyback as these flys seem to be sensitive to over voltages, are there any other "hot spots" I should be looking for with this chassis?

[RCAkid]

Oh, one other item I noticed. I dug through my tube collection and found a good 6KE8 to replace the improper 6GH8A that was erroneously placed on the chroma board (there should only be one on this chassis for the chroma osc). Some things settled down a bit and with a strong signal, was able to attain a very clear picture...except for a couple of things.

There is a faint, vertical, red bar on the right 1/3 of the screen about a quarter of an inch wide running from top to bottom. Additionally, there is a single ghost just offset to the right of the image. Now I have noticed that none of the IF tube have their shields on. I am sure this is having some affect on the signal processing and a dirty tuner I am sure is not helping. The vertical red line is puzzling to me though.

But that could well be solder connections and/or low b+ voltages. Any thoughts are appreciated.

[oldtvman]

on the older RCA sets, always check the resistors in the screen circuit for change in value or burnt resistors.

[Randy Bassham]

I remember one particular RCA IIRC it may have been a CTC-15 or 16, that had a problem with the screen going green intermittently. Apparently the boss had seen this problem before because he came over and poked at a wire that was running along the top of the main chroma/video circuit board. It ran next to a hot resistor and when he pulled up on it it just came into. I'm not sure if by the '21" chassis RCA would have corrected the fault or not. Just a thot....