Following on from part 4, I’ve now tried a newer software version in the 16500A’s EPROMs. Finding a couple of good 27C256s with 200ns access time took a few minutes, but there were no problems with the programming. So, I put them in the CPU board, reinstalled it in the mainframe, and switched on:Oh dear. That’s not good. Without HIL (which is the socket for mouse and keyboard on the front), front panel (which I assume is the spinner knob) or touchscreen, the machine isn’t a lot of use. Must be a compatibility problem with the new software version, I think to myself. Swap in the old ROMs – and the problem is still there. Check the wiring to the front panel, all looks good.

This is annoying. I wasn’t expecting new faults with the hardware. When I next get time to spend on it, I’ll do the obvious checks for bent pins and so on.