The chip enable circuitry for a FM16W08 NVRAMs needs to toggle the /CE for every cycle. The /CE is not grounded so that is a good start. If you want to screw around with it, and me without much thought into it, I would probably lift Pin 1 or pin 2 of the 74HC00 and inject the CLK, /RD or /WR there. Might be all you need to get the FM16W08 working.

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probably so. i think they are enabling the ram like gtb system 3 which does not work with fm16w08 based NVRAMs. In gottlieb system 3 I think it was mixing in the CLK2 into a HC00 got it running with fm16w08. I don't know if its worth trying to hack on a rare board. Maybe use chip socket stacks with bent out legs so you can easily go back to the stock setup.

I've been fooling around with SRAM + super cap on a module board since FM16W08 core chip is still expensive/hard to get. You get a couple months of backup time in most cases and would drop into a board like this and others that don't place nice with FM16W08 directly. Not sure if its really viable solution though. I suppose it would be nice to replace obsolete 5101s with a still in production chip.