Over the past few weeks, I’ve been doing a bunch of repairs on an old Williams System 6 pinball MPU and Driver boards. There were actually two sets of MPU boards to fix and two sets of driver boards to go over. One driver board was known to have problems, and the other was supposedly a gone-over, upgraded, tested-good driver board, which cost a good amount of money. I’ll have a post dedicated to that atrocity shortly.
Anyway, in the process of fixing both MPU boards (neither booted), it just so happened that the MCM5101 SRAM (or 5101 RAM as shown in the Williams schematic) on both boards was bad. This SRAM is the battery-backed memory that saves game settings, high-scores, and other statistics. These chips are not in production anymore and haven’t been for a long time, so obtaining new parts would be tough to do, and supposedly even NOS (New Old Stock) parts could be bad too. This left me with a few options: Hack some other SRAM I had laying around onto the boards, buy someone’s super-expensive (like $30 each) FRAM adapters, or make my own FRAM adapter.

Obviously I chose #3 above, but I did hack on an old SRAM just to make sure that the MCM5101’s were indeed bad. The other non-5101 RAM passed the memory tests in Leon’s test ROM, so the 5101 RAM’s were definitely bad. Now, I was left with making my own FRAM adapter.
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