Well, count me as another idiot.
My friend and I were just handed a HP 9820A, unknown condition.
As usual, the card reader is unhappy, printer unknown, and no display. We took it to bits, and washed everything down. Came out looking great (Magic Eraser worked wonders on the external case).
Power supplies, as usual, are rock-solid and happy.
We _briefly_ got a valid display (0: END |-), after one power
one, but never again.
Clocks are fine, cleaned up some corrosion in a couple of edge
connectors. It obviously _wants_ to live.
So, we will be working on this over the next few months. Thank you to all of you on this forum that have shared your experiences bringing up your gear - it will help. I'll share what we find along the way.