HP "calculators" (was Re: World's first computer on ebay!)

It puzzles me too. The connector in question is a normal, double-sided 25 pin (per side) 0.156" pitch edge connector. That's actually not a common size in the UK (0.156" pitch is not normally used over here), so it's probably somebody 'borrowed' it becuase it was the easiest way to get that sort of connector. The I/O backplane (where this connector whould be) provides 4 idencial slots at the back of the machine for interface models, the PCBs of which plug into those edge connectors. Now, unless you have one of the optional I/O ROMs like 'Peripheral Control) (and this machine didn't come with anything like that, only the maths ROM), these slots are pretty much useless because you can't send data to the interfaces. So removing that connector was probalby not a great loss for the original owner. And as I said it was removed very carefully with no damage tyo the backplane PCB at all. My first guess was that the connector had been used to repair this machine, possibly to replace a damaged conenctor between the memory box and the main backplane. But upon removing the latter, it was clear this was not the case, no other soldering in the machine has been disturbed. Oh well, this is not a major problem in that a suitable replacement part is available, sond soldering it in is not a problem for me. -tony