How to fix and use a 3V lithium coin cell battery with an old A501 Amiga expansion memory - jbilander/HowTos GitHub Wiki

How to fix and use a 3V lithium coin cell battery with an old A501 Amiga expansion memory

Like most A501 memory expansions the battery acid had leaked onto the board and the nasty cadmium had start eating away on the copper.

Cleaning:

Remove affected components, desolder, and clean board with Isopropanol (a.k.a. Isopropyl alcohol or 2-propanol), scraping with a flat screwdriver until clean. Don't be shy using that Isopropanol. You don't want to leave any residues of the cadmium on the board.

Since we are going to use a 3V non-rechargeable lithium coin cell battery we need to block the recharging current from flowing to the coin cell. We do that by replacing the R913 resistor with a 1N4148 DO-35 100V diode with the Anode connected to the Battery's positive terminal.

More about this circuit and the diode mod on my thread on the EAB-forum:
http://eab.abime.net/showthread.php?t=98373

Now with the area cleaned up, time to replace with some new fresh components. Just solder them on there and make sure the tantalum cap bends away from the battery holder

Now time to make sure we get the correct voltages with the new components in place:

  • before R911: 11.94V
  • before D912 (after R911): 5.77V
  • RTC Vdd: 5.21V (after D912, Machine Powered ON)
  • RTC Vdd: 2.78V (Machine Powered OFF, RTC powered only by battery)

That's all folks

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