ZX80 style overlays I do for my Minstrel ZX80 clones. He kindly sent a PCB and CPLD so I could build one.
my Tindie store).
r you can get the overlays and ZX81 membranes from my Tindie store).
Harlequin board I repaired. That had a dodgy 74HC04 chip. I tried a few others here, including the unbuffered version, the 74HCU04 (as used on the Spectrum +2). That didn't help, so I wasn't sure what the issue was. Might have been something up with the crystals I bought. I looked at other series resonant oscillators, and the capacitor value was generally larger, so I swapped out the 100pF for 100nF on the 4.43MHz side and it came to life.
The overlays, membranes, Minstrel ZX80 clones and keyboards are all available from my Tindie store.
If you want to support this blog, you can donate via Patreon or Paypal, or buy something from my store.