RAM chip

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Sony CXK58256 120ns RAM

MVS RAM chips often fry due to overvoltage from a badly adjusted or failing cab power supply. It appears that the most common failure mode is the inability to write new data, resulting in errors during system self-test at the beginning of address ranges.

Basically, all NeoGeo RAM chips with "256" or "257" in their markings are 8-bit 32kB RAMs.

Pinout and cross-refence

To do.

Speed grade

See memory speed.

Replacement

Look for 5 volt, 32kB (32K x 8bit) / 256kbit SRAM (Static RAM) with the right speed grade (most today are 45ns, so any will do) in 28 pin SOIC package. Cypress, ISSI and Lyontek still make them.