The batteries in my TI-89 Titanium drain even while the calculator is turned off. It's second hand so I'm not sure what happened to it in the past but there was some corrosion from batteries leaking. As far as I could see, it was just on the battery terminals and the pads on the PCB that connects to the terminals. I cleaned it up and scrubbed the PCB with isopropyl, though there's still a bit of corrosion around the edges of one the pads.

Weirdly, if I wait until the batteries go flat before replacing them the calculator settings are reset. However, if I just remove one of the batteries and put it back in later the settings are saved.

I connected up a multimeter to measure the current and got:

• 18.75 mA when on and idle on the home screen
  
• 15.2 mA when off
  

I've read suggestions that this could be caused by a short. How would I go about locating where the short is?

That's just the backup battery.

It definitely shouldn't be pulling 15mA when off (should be somewhere around 100μA)
First step would be to clean it but that's already done...
If you can't see anything abnormal just by looking at the board, I guess just measure voltages across the different lines while the calc is off and try to focus on areas where there is corrosion. The power draw varies quite a bit depending on what the calc is doing (notably writing to flash or using the USB port draws significantly more power) so you could try to measure the power draw during different operations like garbage collecting or sending something from the USB port to try to isolate a specific subcircuit.

Oh ok, I had thought the backup battery would also work when the main batteries went flat.



Alright, thanks! I'll have a go and see what I can find.