I have an STfm with one of these motherboards and with the help of my father we succeeded in upgrading it to 4 Mb. The components on these boards are SMT soldered to the board. In stock configuration my STfm only had 512 kb of RAM. This has been SMT soldered in 4x 256Kx4 DRAM's.
I wanted to upgrade this machine to 4 MB, after some googling I found a way to do this on a Acorn Forum
. Some bloke on this forum had the same revision of Atari STfm motherboard and also only 512 KB of RAM. He also shared how he did it. I decided to give it a go and give this STfm the 4 Mb upgrade, which has been a succes
So, I would like to share our experience with upgrading this type of board with the community so more people could eventually do the same upgrade.
Let's start with some practical info, the MMU on this board is a IMP 100109-001, which is also SMT soldered. This type of MMU can only address memorybanks of the same capacity, so possible configurations are:
- 512 KB
- 1 MB
- 2 MB
- 4 MB
A memory configuration of 2,5 MB is not possible with this type of MMU.
To go from 512 KB to 4 MB you need the following:
- 8x 1Mx4 FastPage DRAMs in 20 pin SOJ package. We used TMS444000dj-80 DRAM's, but any type of 1Mx4 SOJ DRAM's can be used as long as they are not faster than 80 ns. We tried 60 ns DRAM's, that didn't work.
- 1x 33 Ohm resistor
- Some wire
- Soldering Iron
- Some courage
There are 4x 256Kx4 DRAM's on the board, these have to be removed from the board. This has to be done carefully, the tracks and solder pads break easily!
Now, after removal of the old DRAM's solder in the new 1Mx4 DRAM's. The new 1Mx4's are pin compatible with the old ones, there is only one difference, pin 5 (MAD9) on each DRAM needs to be connected to pin 64 (MAD9) of the MMU.
Now solder the 33 Ohm resistor to pin 64 of the MMU (careful!) and solder both wires to the other end of the resistor. Use some heat shrink tubing to prevent shorting.
That's basically it. If everything went right and there are no solder bridges or shorts, turn on the ST and load up sysinfo and check the memory, it should say 4 MB.
Here are some pictures of our work:
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