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Corrosion on negative

If there's corrosion on the negative battery terminal, you'll possible have problems with:

  • Power button
  • Shock sensor
  • A button
  • EEPROM (for game saves)

Power button

  • TP2 is continuity to power button.
  • TP2 is connected to two diodes: D5 and D6.
  • D6 goes to the power regulator (the daughter board) to the bottom center pad (there's a via directly between the U1 symbol).
  • D5 goes to the CPU. When looking at the epoxy blob, there's L shaped series of vias (laying on it's back) on the right hand side. The power via is second in from the right (refer to the trace with nets turned on).

Shock sensor

  • The shock sensor is SW2 and pin 1 is the output pin (where pin 2 is tied to ground)
  • The positive leg goes up to the left side of R15 (and then into the CPU)

A button

  • TP1 is a test point for the A button
  • However, the TP1 has more vias to reach the A button than the A button needs to reach the CPU (which is obviously more important)

EEPROM

The read and write data lines have vias just under the negative terminal so if there's corrosion in these vias, games won't save. You'll need a cart that reads and writes to the EEPROM, Pokémon Party Mini is a good test case.

If the mini can't talk to the EEPROM, you'll should a visual error on the LCD saying firstly that the EEPROM is full and then later with an error that reads "EEPROM". The clock should also fail to be set.