I have verified that I can read and write other 27c64s and I also tried swapping ROMS however there is another small glitch. Apparently the HX-20 runs the programs out of RAM. I guess it loads from PROM and runs from RAM. I removed all of the BASIC ROMs and performed a hard reset and when it comes back, it's still running BASIC, without the BASIC ROMs even installed. Wierd! I have looked through the manuals to try and find a way to force a reload but no go (so far). I might try removing the internal batteries and see what happens. The manual also mentions that one can use 27C64s in the HX-20. There may also be one other thing that is causing the problem. I am trying to read the ROMS using family/pin codes for other ROMS. I don't find that part number and have tried a number of other 8K ROM fam/pin codes and none give me anything but blank loads. Perhaps that is part of the problem? Mike
Verify that you can read another 2764 (incase you have reader problems).
Can you swap the 2764 for the Masked ROMs & work without changing jumpers/settings/wiring?
I see there are a few HX-20 collectors on the net, they may be more informed.
Kev
I think I understand what you are saying. I'm sure they are Masked ROMS or at least that would make sense. They are a 4 chip chipset with numbers: EPSON BASIC1R0 M64020AA to M65023AA.
The thing is however, that in identical machines, the other EPROMS are 27C64 so the pinout would seem to have to be the same or the EPROMS would not work right in the other identical machines, would they?