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576 HVPS fixed - sometimes it's simple

Ed Breya
 

I finally got a chance to look at this unit, that had no CRT display. There was no HV. All the LV supplies are OK. After worrying about the transformer (it's the newer good kind with black silicone potting) and other HV parts, I figured on having some major issues. Checking through the various circuitry, I found Q859 (151-0219) was shot. I'm at the farm, and my stock of components is very limited here, but fortunately I brought some boxes of 576/577 parts to sort out - but not including a HV board, which I've misplaced. I found a fresh 0219 on one of the other spare board types, and popped it in, and the 576 lit right up, all good.

Although Murphy's Law would predict a bad supply cap deep inside, or worse, a bad CRT or HV transformer, or other HV parts that I didn't have on hand here, sometimes it turns out to be simple. Once diagnosed, the hardest part turned out to be getting the Q's leads jammed into the ancient socket - these things really have a tight grip. After crumpling up the leads a couple times, I had to clip the their tips to chisel-points to help.

So now that it's alive again, I'll take this opportunity to fix some other issues that have been waiting for years - replacing that wet Ta cap (started to leak) on the PS board with plastic ones, fixing an annoying random offset in the vertical 1-2-5 gain steps (likely dirty contacts on a Printact relay), and maybe fixing the looping compensation shaft, if I can get at it without too much grief.

Ed