I am an owner of the NuPowr 167MHz 603e cpu card for the PowerBook 500 series with no onboard RAM.
I think has a faulty ram slot (and maybe busted capacitors). It used to work fine but now basically mostly doesn't boot. Since it has no onboard RAM, no boot is possible without the RAM being correctly detected in the RAM slot. Only very rarely when it does boot, most of the time a corrupted chime can be heard. As of late I had to press down on the keyboard once before turning it on to get it to boot and make a clean chime sound, though it would often be unstable.
I have had the corrupted chime issue with faulty ram on other macs which makes me think it's a memory-related issue.
I had also noticed that pressing the RAM slot to the side would increase the chances of getting a clean chime. However now most of the time no sound at all can be heard and obviously no boot.
I have tried two other ram sticks which I have tested fine on another powerbook 500 so it's not that but probably the ram slot (like I said i often had to press down on the keyboard to get it to boot so possibly mechanical force influencing the connection). Likely the RAM slot needs to be reseated or resoldered.
Is this something that anybody could /diagnose/repair for a fee? Ideally in Europe?