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  #16  
Old 06-12-2018, 09:15 AM
old_coot88 old_coot88 is offline
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Quote:
Originally Posted by Penthode View Post
As to experiment to remove it, I might try wrapping a few turns of one end of an insulated wire around one of wires leading to the horizontal deflection coil leads and connecting the other to the CRT grid. This would effectively couple the retrace pulse to the grid to cutoff the tube. This may take a bit of experimentation and polarity is important so you would have to try each lead.
Sounds like a great idea. I did a similar 'gimmick' to derive the AGC keying pulse when rigging a non-standard flyback that lacked the pulse winding.

But here, it'd be treatment for a drive bar, and drive bar has already been ruled out. Or maybe I'm missing something..
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  #17  
Old 06-12-2018, 10:05 AM
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old_tv_nut old_tv_nut is offline
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I don't think the added grid pulse is a treatment for a drive bar, which, if I understand correctly, occurs during trace, not retrace. The grid blanking pulse acts during retrace.
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  #18  
Old 06-12-2018, 01:47 PM
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It moves with the horizontal hold adjustment as well.
Does it move more than the picture and in the opposite direction of the picture, when you turn the horizontal hold? If it does, that indicates it's happening during horizontal retrace, so not a drive line.
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  #19  
Old 06-18-2018, 12:13 PM
kramden66 kramden66 is offline
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I have a 64 zenith that has the same thing , yes it moves with horz hold and yes it changes or tries to go away with fine tuning , it will go away completely if you turn the peak picture to make the image softer , I just say the heck with it because it's not anoying , the tv a 61 or 62 zenith had one too but it was very light.
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  #20  
Old 06-19-2018, 12:59 PM
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Penthode Penthode is offline
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I believe the line is a function of the cheaper consumer baseband analog sync generation. The sync pulse edges have too fast rise and fall times and the video peaking to secure sharp edges in absence of later B&W sets video bandwidth (2.5 to 3.0 MHz) exacerbates the problem.

Late 50's, early 60's B&W sets seem to be the worst offenders. My late 40's RCA B&W sets with 4MHz full bandwidth have no problem in this regard.

A minor modification adding a horizontal retrace blanking circuit should fix this. Or using a device which generates sync following the 140ns +/- 20ns rise and fall times of the SMPTE 170M specification.
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Last edited by Penthode; 06-19-2018 at 01:12 PM.
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  #21  
Old 06-19-2018, 01:13 PM
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I added a comment to the drawing pointing out the sync element causing the white line.
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