ZX Spectrum

This machine was the first computer that I actually owned!  My Father and I built a ZX81 when it first came out and then I was lucky enough to get this machine for Christmas in 1983.

It provided quite a few years of good service, before failing.  The machine appeared to work properly until one of the keys on the bottom row were pressed.  This would result in the machine resetting.  I had a go at repairing it when it first broke down - but was unsuccessful (Actually, I did more harm than good - shudder) and I used my saved pocket money to buy myself a Spectrum Plus.  The original Rubber Keyed model was placed in a cupboard and forgotten about.

Armed with a little more knowledge, I decided to have another go at repairing the computer.  The keyboard was quickly ruled out as being the cause - but suspiciously each of the keys which caused a reset were traced to one address line!  (Caps lock, Z, X, C and V) I verified that the problem didn't lie with the ULA by swapping it with the ULA from my Spectrum plus (also not working) but that made no difference - which was a good thing, because the ULA is the only chip that isn't easily replaceable.  Having verified the rest of the glue logic, about the only thing left was the processor.

Having removed the processor, (which was an NEC Z80 clone, rather than a Zilog part) it was replaced with a socket and a new processor.  At the same time, the electrolytic capacitors on the PCB were replaced as these are all around 30 years old and therefore suspect.

With these components replaced, the machine was tested and found to be working!  I was then able to play some of the games that I remembered from my childhood.