Mostek MK8022

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The Mostek MK8022 is a 256 Kbyte QBUS main 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.