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#1
08-03-2004, 10:27 PM
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VT-71 vertical jitters
My motorola vt-71(TS-4H chassis) has verical jitters when it warms up.The vertical control has no effect on the jitters.The set has had a full recap and all high value resistors and all ceramics replaced in the output section.I have tried different 6sl7's,all were good.I have also tried different 12sn7's, all with the same result.
Any ideas????  BTW- I did not use any ceramics for the coupling. 
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#2
08-04-2004, 06:07 AM
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Sometimes horizontal signal inadvertantly mixing in with the vertical signal can cause vertical jitter. In a color set this can happen in the convergence or pincushion circuit...of course this set does not use those, but see if there is any way horiz. signal could be mixing in with the vertical.
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#3
08-04-2004, 12:00 PM
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This must be a real common problem with these. There is at least one other thread here about it. My VT-71 does it, after running for a good while, but so far I haven't taken the time to figure out why.
__________________
Bryan
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#5
08-04-2004, 08:57 PM
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Nope, I did not use ceramics for any of the HV coupling capacitors.
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#6
08-04-2004, 11:08 PM
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if I were you, try adjusting the copper spring that is on the HV rectifier tube while the set is on, and look at the picture as you adjust.
I had to do this, as my picture had those rolling swirly lines causing the picture to bounce around. I adjusted that, and it cleared up.
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#7
08-04-2004, 11:14 PM
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ill try to explain this the best way I can.
I noticed in these sets, especially mine. The HV circuitry and oscillator is seperate from the horiz osc and output stages. most TVs the HV and horiz are together sharing one common oscillator and output. this one isnt. What can happen I think, is the HV osc can run at a slightly different frequency timing than the horiz, and will cause unstable pictures. Ive noticed not only has that feedback spring change the brightness of the picture, it changes the frequency that the HV is oscillating at. so the picture might be abit unstable if the HV osc is not timed right. i may be off a little, but the concept is right.
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