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  #1  
Old 02-10-2019, 03:01 AM
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No color on an RCA CTC-16

Hi, I have had a CTC-16 for little while. When I first got it, it worked poorly and had no color. I checked all tubes, replaced some, and replaced the electrolytic capacitors. Set worked better but still no color. Today, I went and replaced all of the paper style capacitors. Set works even better but still no color.

Color killer control on the back, and the color control on the front have no effect. I have messed with the fine tuning and not even a hint of color. Next step I think I will replace the crystal, then maybe start checking resistors on the color board.

Any thoughts? Anything I am missing? Thanks!
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Old 02-10-2019, 12:47 PM
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Other then the crystal don't forget the circuit boards grounds and traces, and also the tube sockets break away from the solder joint to the traces. Tube socket pins break as well, look very closely . There also maybe wire jumpers on the boards that break and or corrode and the connection is lost .
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Old 02-10-2019, 04:18 PM
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Quote:
Originally Posted by Jon F View Post
. Next step I think I will replace the crystal,...

Any thoughts? Anything I am missing? Thanks!
If the crystal is bad, it won't cause a total 'no color' condition. It'll cause either loss of color sync (barberpoling) or kill the oscillator completely. If the osc is dead, the chroma signal will still appear in the picture, but as pure green, and it will vary normally as you turn the color control.

Total loss of color indicates the chroma signal isn't getting through at all. I would look at the chroma bandpass and burst areas first (loss of the burst signal will cut off the bandpass stage). If the bandpass and burst tubes are known good, check voltages on them against the schematic.
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Old 02-10-2019, 09:00 PM
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Thanks for the advice. I inspected the board today, and checked voltages as suggested. The chroma bandpass and burst sections seemed good, +/- 10% or so. (some voltages required the color killer control to be adjusted to be in spec)

However, on the 6JU8 color killer detect & chroma sync phase detect I found some low voltages, see attachment. Where it is labeled 50V or -50V I found about +/-3V and +/-9V

Any thoughts? I checked a bunch of resistors around this tube they all measured OK.
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File Type: jpg Screen Shot 2019-02-10 at 5.55.14 PM.jpg (89.9 KB, 24 views)

Last edited by Jon F; 02-10-2019 at 09:20 PM.
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Old 02-10-2019, 09:46 PM
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For the heck of it, try grounding point 'E' and see if you get any chroma going thru.
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Old 02-10-2019, 10:18 PM
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Quote:
Originally Posted by old_coot88 View Post
For the heck of it, try grounding point 'E' and see if you get any chroma going thru.
Yes.

Assuming V11 and its connections are OK, you are probably missing either the oscillator CW on pins 2 and 8 or the color burst inputs on pins 1,3,7,9. As noted above, a dead oscillator should give a green-tinged image, so it's more likely the burst is missing. A scope would give a quick check on which it is.
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Old 02-10-2019, 10:38 PM
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Quote:
Originally Posted by old_coot88 View Post
For the heck of it, try grounding point 'E' and see if you get any chroma going thru.
No chroma. The picture gets slightly darker but that's it.

Added some more voltage measures:
Attached Images
File Type: jpg Screen Shot 2019-02-10 at 8.39.18 PM.jpg (96.0 KB, 19 views)
File Type: png Screen Shot 2019-02-10 at 8.39.24 PM.png (113.0 KB, 17 views)

Last edited by Jon F; 02-10-2019 at 11:40 PM.
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Old 02-10-2019, 11:57 PM
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I'd swap the burst amp tube just for spits 'n giggles. it brought back the color on my CTC21
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Old 02-11-2019, 12:09 AM
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Originally Posted by mr_rye89 View Post
I'd swap the burst amp tube just for spits 'n giggles. it brought back the color on my CTC21
Thanks, however I have already tried swapping around the burst amp 6EW6 as well as the band pass, color killer detect, etc just to be sure.
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Old 02-11-2019, 12:27 AM
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Quote:
Originally Posted by old_tv_nut View Post
Yes.

Assuming V11 and its connections are OK, you are probably missing either the oscillator CW on pins 2 and 8 or the color burst inputs on pins 1,3,7,9. As noted above, a dead oscillator should give a green-tinged image, so it's more likely the burst is missing. A scope would give a quick check on which it is.
The image is not green, completely black and white. If I am missing color burst inputs, any idea what it could be? Or just trace the schematic and see if I find anything?
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Old 02-11-2019, 01:20 PM
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Are you sure the chroma bandpass amp plate is the same voltage as the screen grid (148 v)? That's not right, for starters.
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Old 02-11-2019, 02:49 PM
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That is very strange, your plate voltage should not be that low ( looking at the SAMMS for your TV, ) point 108 into r156 ,at 260v or near that (unlikely that it's not ) point 90 ( before into L25 ) should be 255v ish, Out of L25 (at 8.8 ohms ) there should be little voltage loss.
-4.9v on g1, normal, 148v g2 , normal, even if there is no signal out of L24, v17a should not be in a full on state, so there must be a loss of voltage between the power point ( r156 or l25 ) or somehow there is a short from plate to 2nd grid ( very weird )
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Old 02-11-2019, 08:37 PM
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oscilloscope is your friend

Quote:
Originally Posted by Jon F View Post
Hi, I have had a CTC-16 for little while. When I first got it, it worked poorly and had no color. I checked all tubes, replaced some, and replaced the electrolytic capacitors. Set worked better but still no color. Today, I went and replaced all of the paper style capacitors. Set works even better but still no color.

Color killer control on the back, and the color control on the front have no effect. I have messed with the fine tuning and not even a hint of color. Next step I think I will replace the crystal, then maybe start checking resistors on the color board.

Any thoughts? Anything I am missing? Thanks!
At some point an oscilloscope is the best and easiest way to pin down problems like this.
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Old 02-12-2019, 12:21 PM
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Quote:
Originally Posted by old_tv_nut View Post
Are you sure the chroma bandpass amp plate is the same voltage as the screen grid (148 v)? That's not right, for starters.
I copy-pasted the 148V from pin 3, pin 6 should have read 268V. I updated the image below.

Quote:
Originally Posted by oldtvman View Post
At some point an oscilloscope is the best and easiest way to pin down problems like this.
I have a scope, but do not use it much so my skills in diagnosing a TV with it are limited. Any tips on waveforms I should check?
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File Type: jpg Screen Shot 2019-02-12 at 9.18.25 AM.jpg (97.7 KB, 15 views)

Last edited by Jon F; 02-12-2019 at 12:30 PM.
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Old 02-12-2019, 12:45 PM
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Then at this point, as oldtvman said, you won't get far w/o an ntsc color bar generator & an o-scope, cause if what you show is true, V17a is in a normal state, so the input needs to be checked, but w/o a color bar input ( to look for the bottom waveform shown with the circle) it will be very hard to progress without it using just standard video input.
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