Mostek MK8022

The Mostek MK8022 is a 256 Kbyte QBUS memory card in a dual QBUS card-size format, using 64Kx1 DRAMs.

No documentation is currently known for this card, but since this card has two banks (i.e. it has a 9x4 array of xx64 64Kx1 chips; i.e. to provide 16 bits wide plus byte parity, there are two groups of 18 chips), it is sometimes possible to repair problems in one.

If one bank is picking or dropping bit(s), and the other is not, that meant that data paths were all OK, and it is a simple matter of finding the bad memory chips.

By pulling memory chips (luckily, they were socketed on the board of this type which was examined, so this was pretty painless), it was possible to work out which bits are stored in which chips. (Unlike many memory cards, it's not semi-random.)

Low bank:

Bit	Chip
01	H1
...
0200	H8
0400	E1
...
0100000	E8

High bank:

Bit	Chip
01	F1
...
0200	F8
0400	D1
...
0100000	D8

D9-H9 seem to be parity.