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!

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 .

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.

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.

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.

No chroma. The picture gets slightly darker but that's it.

Added some more voltage measures:

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.

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?

Are you sure the chroma bandpass amp plate is the same voltage as the screen grid (148 v)? That's not right, for starters.

That is very strange, your plate voltage should not be that low :o ( 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 )

oscilloscope is your friend
 

At some point an oscilloscope is the best and easiest way to pin down problems like this.

I copy-pasted the 148V from pin 3, pin 6 should have read 268V. I updated the image below.

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?

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.

According to the schematic, there should be about 5 volts difference across R154 (260 V on supply side, dropped to 255 V at the plate of chroma bandpass). You could measure the supply and the plate voltage and see if they are 5 volts different. When the color killer operates, the bandpass amp is cut off and there will be no drop.

So, go back to grounding point E. This should defeat the color killer and let the bandpass amp conduct. Turn the color control all the way up and see if you see any color.

As far as using the scope, set the scope sweep rate to horizontal sweep rate (about 10 microseconds per division). For starters, set the vertical sensitivity to 10 volts per division (or 1 volt if you have a 10X probe) and check for presence of all the waveforms shown in the SAMS schematic for the chroma sync phase detector and color killer, plus the chroma bandpass. Set the vertical to higher gain to view the smaller waveforms that are marked about 10 or 12 volts peak to peak.

Do you have a color bar test pattern to use, or are you using some program video? The chroma waveform on pin 3 of coil A14 will generally not be as big and obvious with program material as with a test pattern, but you should be able to see it come and go when the color killer operates.

Also look for the chroma at point G, pin 1 of V23 X demodulator (or pin 1 of V21, Z demodulator).

Thanks for all of the advice guys. I haven't pulled out the scope yet but have some good news. I did the "color afc alignment" procedure which only requires a voltmeter and now I can get very weak color. The alignment settings were not really that far off, so I am not sure if I tweaked it just enough to get a weak color signal and there is still an issue somewhere.

There is only a color image at the counterclockwise end of the fine tuning of the channel. It is also pretty difficult to get the color and picture stable at the end of the range. I have had trouble getting the color bars to sync properly as well.

I have a portable color bar generator, see attachments.

I was watching the TV today for a little bit, but out of nowhere something else happened.

The screen is now red, brightness control doesn't really do anything. HV is down to ~18kV. Cathode current on 6JE6 runs high after the TV warms up. My initial thoughts are a loose connection or cracked solder joint.

If you haven't already done so, re-flow the two ground stakes on the far right end of the chroma board. If one of those goes open, it kills the heaters on the 6GU7s. Their plates go high, and since the plates are DC-coupled to the CRT grids, beam current goes out the roof, dragging the HV down. Also 6JE6 cathode current goes high.

This may not be what's causing your problem, but always reflow those stakes anyway. It's an endemic problem to CTC-12, '15, '16, '17, and '25.

Thanks for the tip, I have reflowed these points. Powered up the TV this morning and still has the same issue.

Even though you have re-flowed these points, check the 6GU7s while the set is turned on to see if their filaments are lighting up.

The filaments do light up

Well I just reseated a bunch of tubes and now the problem is gone. I can’t seem to replicate it unfortunately.

One of the things I found was a connecting wire that was located around the area in question. It seemed to be affected by the heat of the tubes and the larger resistors. It seemed to arc and destroyed the 620mh peaking coils.
The first thing I did was remove it and relocate it under the PC board. :thumbsdn:

Is the circled wire in the attachment the one that gave you trouble?

I have also attached a couple more pictures of the set issues in operation. Most of the time when I can get color it doesn't lock in, more of a rainbow. Playing with the horizontal hold or fine tuning sometimes gets the chroma to sync properly.

I have done an experiment where I pull the chroma oscillator tube out during operation, let the tube cool down, and then put it back while the set is on. While the tube is warming up there is a point for a few second where the chroma locks in. However, after the tube is fully warmed up it becomes a rainbow again.

Also, having a little bit of trouble with horizontal sync in general as the vertical lines in the cross hatch are difficult to adjust to be straight.

If the chroma osc has a broad lock in adjustment range I typically connect a color bar generator and with the color maxed adjust the fine tuning till the color is barely there (and hold the color osc in sync). The lock point should be smaller but still exist. Then I rock the channel selector and see if it holds sync, and tweak it so that it locks as fast as it can between channels with minimal color signal...If it will lock under those conditions normal viewing signal levels and finetuning position will be a piece of cake for it to lock to.

If it can only lock to strong color there are probably circuit issues or bad alignment problems.

That's the one. I see the other that gives trouble has already been replaced. Also the peaking coil has been jumpered out. Try to replace it if possible.

Regarding the horizontal wiggles, two things could contribute:
1) Your color bar generator probably has a simple vertical sync pulse with no serrations; that interrupts the horizontal sync. This causes the horizontal AFC detector to output an erroneous voltage during V sync; then it has to recover.
2) The R and/or C values in the horizontal AFC filter circuit (between the detector and the oscillator) are off, causing an undamped, ringing response.

A possible third minor contribution could come from the sync separator itself, which is shown by the slight wiggle on every row. This may be normal for this set with this bar generator. I have seen it often on sets that otherwise operate fine with a standard video program source. It could also be affected by fine tuning.

Both of my dot-bar generators exhibit the same behavior.

If you have the schematic and it appears you do, it should show waveforms for different points of the set. I know Sams has waveform pictures based on using a color bar generator.

Even if he doesn't the ETF has the CTC-16 sam's in free PDFs on it's site.
http://www.earlytelevision.org/tv_sc...ams_color.html

That chassis may have lots of cold joints. Like tube sockets, common.

Most of the time when I had this problem I would always check the plate voltage on the chroma tubes and usually sure enough, one of the shielded coils would be open and that would kill the color. Many times you can fix the coil due to a bad solder joint on the coil.

Hi all, I've been a little distracted at work lately. However I have since bought a blonder tongue RF modulator and this has helped the color sync much easier.

I am still have issues with waviness at the top of the image. Same whether is the line generator, or laserdisc player. Next step is to pull the chassis again and reflow many connections.

May want to scope your H sync line and see if it is clean/strong or noisy/weak. If noisy focus on sync sep, if clean focus on H AFC diodes/components around them, osc, and feedback from the fly...

I assume you've followed the sam's horizontal setup procedure for your chassis...If not please slap your forehead, then do it. :D

Have you tried adjusting the AGC?

I’ve done the horizontal setup twice and adjusted the AGC :)

I finally pulled the chassis and reflowed the connections on the sweep board. This fixed the issue. I visually found 2 that weren’t connected.

I am still seeing 2 things,

1) “Contrast” streaks as shown in the picture
2) The image slightly waves left & right. Almost not noticeable. Maybe something isn’t grounded?

Any thoughts?

I get that too ( very slightly ) no idea what it is...

I have no sure ideas, just some random thoughts on looking for the streaking.

1) Does the streaking change if you adjust fine tuning? (would indicate problem in IF) I'm guessing not.
2) does the streaking change when you exercise the video peaking switch?
3) check voltages in the video stages
4) is the capacitor on the video output screen grid (schematic not clear, but looks like .22 uF) OK?