Amiga A500 Slow RAM with SIMM modules

I was thinking about the trapdoor ram expansion and found 4 old SIMM modules.

2 of them where identical

Chip = GM71c4400 2MBx4Bit

SIMM = 2MBx8Bit

The third memory ic is for the parity bits

(not used here)

I need at least 2 SIMMs for the 16Bit data bus.

Googling around and found that an official expansion exist to use SIMM as trapdoor ram.

While searching for SIMM and Amiga pinouts,

I found this one

made by John Tsiombikas.

I thing it is simple and enough

so i build it my self :-)

My flux is not the best for this kind of work

Remember that i need 2 SIMMs?

what a messy wiring job.

Hopefully this PCB is working!

Update:

One of my SIMM modules was faulty, i changed it and now i have 512Kb Chip Ram and 512Kb Slow Ram.

Links and Downloads:

- Amiga A500 schematic -

- John Tsiombikas -

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