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November 22, 2020 10:34
November 22, 2020 10:34
December 19, 2021 23:20
December 19, 2021 23:46
November 22, 2020 10:34

Atari 520ST(M)
4MB RAM Expansion

Tested on C070243 Rev.I , your mileage may vary.


  1. The board needs fixing with a bodge wire

  2. The expansion board must be installed
    directly onto the motherboard.

    Using sockets won't leave enough
    clearance for the keyboard


Component Value Size Package
C1 - C6 100nF 0805
R1 - R2 68Ω 0805
R3 33Ω 0805
2x 5118160 DRAM SOJ42


  • De-solder the existing RAM.

  • Solder the expansion board in place.

  • Solder the four wires from the expansion
    board to the motherboard.

    Signals: MAD9, CAS1L, CAS1H, RAS1

    MAD9 can usually only be found on the MMU

    The CAS & RAS pins can be soldered to on the
    underside of the motherboard as well as,
    on some boards, on the topside as well.

    Name MMU Pin
    RAS1 18
    CAS1L 21
    CAS1H 22
    MAD9 64