Sinclair ZX80 / ZX81 / Z88 Forums

Hi everyone.
Just getting back into 80's computers and trying to put together a collection of the machines I wanted at the time.

Had one of the first zx81's back in the day but gave it away many years ago. I then ended up working in a nuclear power station, writing reactor control software in CUTLASS and maintaining Honeywell DPS 6 supermini's and 8086/80286 target control computers. The amazing thing is, they are all still there and working !

Have a issue 1 zx81 needing repair, so may ask for some help. ULA is giving a clock signal and a blank video signal, but the processor isn't running

Also got

BBC B (fully working)
Spectrum (now fixed)
Apple ii eruoplus with z80 second processor (in need of tlc)
TRS80 series 4 (currently on shelf at work where it's been for 35 years, in process of being liberated)
3032 commodore PET (fully working, case needs a spray job)

Wanted
RM-380Z (pipe dream ?)
Memotech MTX-512

Hello Gary C,

welcome to our crazy club... bear in mind some of us are crazy also anyway you've come to the right place for some help with the hunble 81.

you say the ULA is giving a clock signal but is it getting to the cpu? check pin 6 at the cpu, it is an inverted signal from the ula , been inverted by tr2.

regards Andy

Hi Garry C.

Welcome, Garry!

For fixing your ZX81, what tools you have available? Scope or even a simple logic probe would be very helpful. Any other ZX81's in your possession that you could swap parts with?

Usually ZX81's are easy to fix, with 2 exceptions:

• ULA itself. If that's dead (or its video output blown), there isn't much you can do. Some modern ULA replacements are out there, though.
• Keyboard. But you can buy replacement keyboard foils. And some die-hards like on here have built their own keyboard for the Zeddy.

In other words like a classic car: if you want it enough, it CAN be fixed.

Hello Gary

Welcome to our forum

Please take a look around. There are gems of information everywhere. And if you have a question, please ask.

Mark