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#16
12-06-2015, 05:10 PM
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Is there any snow in the picture, or only a raster?
This TV has split sound - the sound picks off the plate of the 1st video IF. So your signal is at least getting through the first video IF amp. I guess I'd try changing the 2nd and 3rd IF tubes, and the video detector. Next measure voltages on those socket pins. 
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#17
12-08-2015, 06:39 PM
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Ok, after changing both the 2nd and 3rd IF tubes, I now have a video signal. It's not good, and the audio is still distorted. The 20uf electrolytic in the audio came in, but that didn't help. I'm still waiting on a 16uf filter in the focus coil circuit.
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#18
12-09-2015, 11:19 AM
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Quote:
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#19
12-09-2015, 11:49 AM
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Assuming direct video in gives a good sharp image, then it looks like somebody may have twiddled with the IFs.
Last edited by old_coot88; 12-09-2015 at 12:16 PM.
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#20
12-11-2015, 04:47 PM
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I think I've got the picture as good as I can get, but the sound is still somewhat distorted.
It sounds like an intercarrier buzz which tweeking the audio Ifs will not get rid of. Any ideas on how to clear up the audio?
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#21
12-11-2015, 04:56 PM
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There is no intercarrier, so that can't be the source of the buzz. Are you using a balun? Try connecting the 75 ohm coax directly.
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#22
12-11-2015, 06:09 PM
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Did you try it yet?
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#24
01-08-2016, 08:27 PM
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Another problem has developed. The horizontal is very unstable. Sometimes, I cannot even get it to sync even though besides the hold control, there is a trimmer for a horizontal lock, drive, freq, and a coil for the horiz lin.
I left the set on for 20 min while I was troubleshooting, and the width shrunk and no sync was the result. See pic
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#25
01-20-2016, 04:26 PM
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I have now lost the raster completely. I finished replacing the mica caps in the horiz osc section as well as resistors. Voltages on the 6SN7 check ok. Tried another 6Sn7 as well as a 6BG6 output and 1B3. Any ideas? Here is the horiz section on the schematic.
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#26
01-20-2016, 04:47 PM
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Well if it quit after you changed the Micas I see two possibilities.
1. You got something wrong.  2. The values are different from the originals, possibly because the originals were bad, now the frequency is so far off the oscillator won't run. Try adjusting the H Osc coil.
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#27
01-20-2016, 05:06 PM
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Eric, that post was confusing. The raster quit while the set was playing. I then replaced 3 micas hoping one of them had gone bad.
First, the horizontal lost stability, then I lost sync altogether. Next the pic shrunk (see pic 2 posts ago) then I lost the raster completely.
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#28
01-20-2016, 05:14 PM
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If you Have a scope check and calibrate (by comparing the freq to video synch) the osc. If that don't fix it check voltages on the H out tube, and if those are fine check the damper tube. A shorted or weak damper will kill the raster.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#29
01-20-2016, 06:42 PM
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I don't have a scope, so I checked the voltages on the 5V4 Damper. Pin 2 is low about 45V. I don't have another 5V4, but my tube substitution guide says a 5U4 will sub. I want to make sure of that, then I will try a 5u4 in it's place.
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#30
01-20-2016, 08:54 PM
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My Dumont uses a 5U4 for a damper, and this set seems to be a dumont inspired design so it will probably work.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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