Sinclair ZX81

Around 1982, I got my very first home computer, a ZX81. I learned how to program computers on it.

Unfortunately my original ZX81 does not exist any more. I broke it by attempting to do hardware modificiations, and eventually disposed it. Today I regret that I haven't shown more respect to my first computer.

I found this ZX81 at an online auction. It is in a good optical condition, and is looking very similar to the system I once had myself. This is why I bought it. According to the seller, it was assumed to be in working order, but untested.

The 16K RAM expansion that was sold along with this ZX81 was said to be definitely broken. It turned out that the seller was correct, as the RAM expansion had a broken ULA chip and couldn't be repaired. Luckily I have found a similar RAM expansion at another auction, so the set is complete and working now.

Configuration

• Built: Around 1983/1984
• Mainboard: Issue 3
• CPU: Z80A
• ULA: 2C210E (date code 8312)
• RAM: 1KB (internal), 16KB (expansion)
• Composite Mod

Restauration Works

• Restauration was carried out in December 2021
• Case cleaned
• Modified the modulator to create a composite signal, reversible
• All electrolytic capacitors replaced with new, long-live types
• Replaced 7805 with Traco Power TSR-1 DC/DC converter, and removed heatsink
• ULA and CPU heatsinked
• Keyboard membrane connector broke off during restauration due to old age, but could be recovered
• Original 16KB RAM expansion could not be repaired and was replaced by another RAM expansion (also recapped)