I thought I would share my experience in getting a ZX81 going
I purchased an untested ZX81 with 16K ram expansion module
When I eventually got around to testing it I soon discovered the untested unit
was in fact faulty. No or extremely weak video was the issue and this meant a
new ULA was required the original ULA was a 2C184E (1st gen i believe) as these are no longer
available a 2C210E was ordered. Once this was fitted the ZX81 was back in action
not having a CRT TV i decided to fit a ZX8CCB at the same time. The picture quality
on my Sony LCD is surprisingly good with this mod. Of course it never ends there.
The keyboard membrane had a crack in the normal spot (under the ram chip).
I know new membranes can be purchased but this meant more delays and more $$.
The pictures show how i fixed this problem and the cool raised keyboard that came with the machine.
First remove the Molex connectors from the PCB then make 2 extensions using ribbon cable
and cut a 16 pin IC socket cut to size(8 pins and 5 pins). Cut the membrane below the crack and fit to the original
connectors these then plug into the IC sockets making removal a lot safer next time.