Atari 520 ST(M) 4MB Memory Upgrade/Expansion

Originally Designed By Anders Granlund from Sweden....

Having fixed this PCB last year, it's becoming increasingly difficult to obtain the original RAM IC's without resorting to reclaiming them from other hardware....

So this is an Alternative option using OKI Semiconductor RAM instead.

Tested on C070243 Rev.I ...

### Important ###

The expansion board **MUST** be installed directly onto the motherboard.

Using sockets **WILL NOT** leave enough clearance for the keyboard!

Parts List...

C1 to C6 | 100nF | 0805 | x6

R1 | 33Ω | 0805 | x1

R2+R3 | 68Ω | 0805 | x2

MSM5118165F DRAM | TSOP-II 44 | x2

Installation

- 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**

Routing the MAD9 Signal through a SPDT switch with one side to ground will allow switching between 1MB and 4MB...

MMU Pin

RAS1 | 18

CAS1L | 21

CAS1H | 22

MAD9 | 64