This machine has worked since 1978 or so, and has indeed been back to HP (who seem to have hams for hands).
Anyway, it was working as I was doing calculations, then quit in a few seconds between the time I set it down and picked it up again, possibly 4 sec or so. As I wasn't watching, I don't know what exactly it did.
No display or response.
It was then disassembled, the broken posts etc reinforced and glued, but still no response. Contact appears to be made to all the pieces.
It has the extra board with CPU etc, and does not appear to have any opens or etc on the display.
Any OTHER ideas? Symptoms (and life) are noticeably lacking!