On 10/21/2021 9:10 AM, Nigel Johnson Ham via cctalk wrote:
Thanks, but like bitsavers they are all older that the one I have. To be honest, I never saw anything Plessey bigger than 128kB in the wild, so I have to wonder what kind of machine this board came from, although it was in a pile of Qbus things that I got the J boards from. I'm thinking that maybe it was not sold separately, but an OEM build for military etc, and perhaps it is jumpered to get power from memory - but without the manual or tracing the lands I can't really tell.
Wait, that could be it: If the board is jumpered to power the memory refresh/chips from battery then of course it wouldn't work without it.
Should be easy to check: Find the battery +5 and +12 pins on the Q bus then use a tester meter to check from those pins to any of the jumper pins. If you find continuity to a jumper that is closed you might have identified the problem :-)
