DECstation 5000/133 power supplies dead (H7826)

Seth Morabito lists at loomcom.com
Sun Oct 1 16:38:04 CDT 2017


All,

I have two DECstation 5000/133s here with dead power supplies. I've done
some basic troubleshooting on both, and I've recapped the other, but
they're still dead dead dead.

I don't see any obviously blown components, and the fuses are fine, but
several of the caps I replaced WERE leaky. I inspected for bad traces
but found none.

So far it looks like the high voltage side is totally fine, but the low
voltage side is completely dead. No activity. Switching transistors SEEM
fine, but I haven't pulled them to check them out of circuit.

Is anyone intimately familiar with the H7826? Any obvious failure modes
I should check?

-Seth
-- 
  Seth Morabito
  lists at loomcom.com


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