I had a ZX-80 with upgraded ROM (to ZX-81) such that the onboard memory (1k) was insufficient to run the memory test program you got with the computer. Luckily,

I had a ZX-80 with upgraded ROM (to ZX-81) such that the onboard memory (1k) was insufficient to run the memory test program you got with the computer. Luckily, I had the 16kB expansion module. The worst part was that my monitor was a US TV set (most Australian TVs didn't have UHF support) but it was NTSC, so to get a usable image I had to do crazy things with the vertical hold.