OOMFIE (Memory board)

[Mustermann]

Bill of Material for OOMFIE:

IC1,IC2,IC3: 3x 74HCT157 SO16 or 3x 74HCT257 SO16 (both will work)
IC4: 1x 74HCT08 SO14
IC5: 1x 74HCT251 SO16
IC6: 1x 74HCT4075 SO14
IC7: 1x 74HCT00 SO14
IC8: 1x 74HCT04 SO14
IC9: 1x 74HCT74 SO14
IC10: 1x DS1210 DIP8
IC11: 1x 128kx8 SRAM, e.g. KM681000ALP DIP32 (not named C11 on the PCB)
C1- C5, C7-C11: 10x 100n 50V 0805 (C6 disappeared at a shrink of the board because of the keyboard connector)
R1-R9: 9x 1k 0603
R10-R13,R15,R16: 6x 10k 0603
R14: 1x 680R 0603
32pin precision IC socket (maybe the RAM needs to be soldered direct into the board to close the lid)
8pin precision IC socket
Pin header: 1x46 e.g. 2x W+P 952-09-036-1 (46pins are needed)
Pin header: 1x2 e.g. 5x pin header 2,54mm 1x2 H=11,6mm BKL 10120914
Battery holder for CR2032 (should be low profile to close the lid)
Battery: 1x CR2032

[Mustermann]

Known limitations:

Does fit only into Timex Sinclair 1000 board (tested) and may be ZX81 issue 3 board (not tested yet)
Does NOT fit into ZX81 issue 1 board

If UDG/WRX jumper is set to WRX, CHR$128 does not work

If ROM overlay is set to something else than off, an external board is not able to deactivate ROM overlay by pulling /ROMCS to high

[Mustermann]

How to build part 1:

First check if you have TS1000 or ZX81 Issue 3 board.

If yes, remove:
R2 680R
R28 680R
R18-26 1k
All RAM chips and RAM sockets

Desolder the pin of D1 at the side where the RAM is located

If C8 and C9 are disk capacitors remove them as well

Ensure that wire bridge is at LK2 position