Hi there,

I've got an old Commodore PC 10 for repair here, it's an early revision.
I was troubleshooting it and learnt a few things I want to share.

If you have original BIOS, # 380204-01, you may encounter issues with EGA/VGA cards and V20 processors.

- The VGA card's BIOS won't be loaded, resulting in a long-short-short beep code sequence and a black monitor.
The BIOS still tries to boot off floppy drive, though.

- The PC seems dead if a V20 processor is plugged in.
Probably because the BIOS used that one x86 instruction not supported by V20/V30.

As a workaround, you can load PC 10 BIOS v2.01 (# 380258-01) or newer.
To do so, you need a bigger EPROM, type 27128 or compatible.

I've used PC 10 BIOS v2.05 so far and it seems to work.

Best wishes,
Jo22

PS: The DIP switch settings on an ancient PC 10 motherboard might be set to MDA by default (for Commodore monochrome board).
Changing it to CGA/80x25 chars might be helpful if a VGA card is in use.