KiCad A572

2MB RAM Expansion for the A570 CD-ROM Drive

This is a simple 2MB RAM expansion as others have done for the A570. It is simply an implementation of the Commodore schematics. People have done these before but frustratingly I couldn't find any gerbers to make my own, hence this implementation.

The PCB layout could be better - feel free to rework it. But as it is, the card is perfectly stable and works well. I used 514400J 1Mx4 SOJ DRAM chips which are easy to find. Interestingly 424400 chips don't work (at least the ones I tried) giving a black / blinking screen, so better to stick with what CBM specified on the schematics.

For the lazy, you can order gerbers from DirtyPCBs or from your own board house (see the releases page), or remix how you like with KiCAD.

If you scrounge old single sided 4MB or dual sided 8MB 72-pin PC SIMMs you will probably find some suitable DRAM.

You will also need a 2x20pin female right angle header, and some decoupling caps. The schematics say 0.33uF but I used 0.1uF with no issues and it even works if you leave the caps off.

The jumper is the RAM enable jumper. Connect it to a wired external switch if you really feel you want to be able to disable the RAM without opening the cover again.

Schematic

Front

Bottom

Connected

Memory Test