- All 8 memory chips are good (16K model)...tested them by creating a rig in my ZX81 16K RAM pack and replaced them one at a time and they all worked
- Memory is getting proper voltages (-5/12/5) and are within specs (within 10% -4.69/11.73/4.85).
- Voltage regulator also proper voltage (8.84 in from regulated 9 volt supply and 4.85 out)
- Tested all onboard capacitors and they seem good
- The screen has black/white bars (did composite mod) with blinking colored blocks: a couple of people during that German online conference told me it is likely not the ULA
- Removing ROM doesn't seem to change display
If not the ULA and ROM, there isn't much left. Just the a chip for the TV modulator and two chips that seem to control the upper memory. Could it be the CPU? I have a spare ZX81 with socketed Z80 which I could use (just have to unsolder the ZX Spectrum's Z80 which won't be that bad. Any ideas would be helpful...