Point zero - where we came from and what we have now

A project log for "Master" restoration

Put Soviet ZX-80 clone back to life

Fedor GruzdevFedor Gruzdev 01/18/2022 at 23:040 Comments

In the very beginning...

When I've bought this thing, I had a thought: "Hey, this could even work the first time!" Of course, that was not the case. Opening the case has shown nothing interesting (even no leaked electrolytes!), but first things first - I needed to connect it to power supply. Unfortunately, neither I had a TV or anything else to check RGB output nor the computer had a buzzer to produce sounds (which got me time to find out, heh). So the project was shelved for the first time.

Fast-forward some amount of time: I've acquried small analog input display (like 7" or so) and found a schematic for machine. So I cobbled together an 5-pin-to-RCA-jack adapter for video and tried connecting everything together. Image appears! But, for the second time, it does not behave properly - no sense can be made of it (just random color squares on the screen). So I decided to replace video driver IC (which also handles everything else including keyboard and sound).

It failed with the same symptoms. Then there was ROM, something 27C16-compatible. Desoldering and dumping it gave possible culprit - ROM was empty. How (it's factory masked truly read-only memory)? I don't know. Unfortunately, while this particular ROM can be bought on a second-hand markets, I couldn't obtain one.

And so we're left with a board without ROM in unknown state. Time to go on!