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  #16  
Old 02-12-2019, 01:04 PM
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old_tv_nut old_tv_nut is offline
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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).
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  #17  
Old 02-13-2019, 02:08 AM
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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.
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  #18  
Old Today, 02:05 AM
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Jon F Jon F is offline
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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.
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  #19  
Old Today, 10:43 AM
old_coot88 old_coot88 is offline
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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.
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