I have a Yamaha FX500 effects processor which I bought new in 1989.

The original backup battery has been holding out all these years to this day, believe it or not.

Pending the succesful batteryless mod I did a few weeks ago on my ADA MP-1, I decided to do the same to the FX-500.

The FX-500 drives its 8x8K SRAM chip a little differently from the way it's done in the MP-1. This mod requires that one of the signals be inverted and sent into a different pin, requiring a more complicated circuit. Whereas I built the chip daughterboard for the ADA MP-1 using generic stripboard, for this more complicated job I decided to make a custom PCB in order to keep it compact.

Also, before doing anything, I had to desolder the original SRAM, which Yamaha mounted straight to the circuit board, and put in a 28 pin socket. This socket lets us insert our daughterboard and go back to the SRAM chip easily if that doesn't work. We don't want to be soldering our work to the circuit board; not to mention that the header pins would require us to drill out to 35 mils, which would destroy the plated through holes.

It works great. The battery is gone, and the FX-500 is retaining everything.


Pics:

 

Etched, Drilled Board: Toner Resist Removed:
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Assembled: Installed in FX-500, and removed the battery:
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