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Originally Posted by Penthode
1. Which +285V is being pulled down: the +285V IF or the other +285V supply feeding the vertical centering control?
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Here's a rundown of voltages:
Mains input set at 116 with RCA Isotap.
Main 400v: 380
IF (coming from pin 2 of the ballast): 300
285 supply going to vert centering control: 260
As read at the filter cap of each respective line.
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2. Did you change the rectifiers to silicon?
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Yes I swapped some in briefly for a test, made no difference so I changed it back. Stock seleniums are still connected.
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3. Have you tried putting back the old electrolytics for a test?
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You mean the chassis originals? They are totally shot (open circuit), so no point.
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4. What did you last do before the problem appeared? (Did you see the problem before changing the electrolytics?)
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I didn't change or do anything really, just moved it from one room to another and it worked fine in the new room for a spell then this popped up for no reason.
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5. What basis do you think the ballast too hot? (Between the two resistors, the ballast is going to dissipate close to 50 watts which will make it pretty darn hot!)
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Hot enough to produce smoke, I'm not willing to let it go any longer than that...
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My long shot guess is that if the capacitor impedance has changed maybe you are seeing the rectifiers switch on the screen?
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I don't think it works like that with seleniums, but I could be wrong. Something about this set changed in a bad way to make this start happening, it was working fine one minute, the next it's all jacked up. I just haven't been able to track down the source yet.