MB-02+ 512k SRAM, single chip
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- dismantle MB-02+, pull out PCB from case, remove backup battery and original SRAM
- bend pins 1, 22 and 30 on 512k SRAM chip 
- solder BAT43 diode and 2k7 resistor (10k in schematic) to pin 22 (see photo)
- the other end of diode connect with /ENRWM (IO18 pin 15)
- the other end of resistor connect with RAMUCC (joint of R10 and T2 collector)
- connect pin 1 with PG4 (IO18 pin 13)
- connect pin 30 with PG3 (IO18 pin 14)
- put 512k SRAM into socket
- insert battery
- assemble MB-02+ 

Done!