RTC circuit in Amiga 3000T

[nscaleworld]

I would like to do the CR2032 coin battery install in my Amiga 3000T.  I was wondering if I could desolder and remove R192 and replace it with a 1N60 diode.  Also, I noticed that there is both +5 volts and +12volts in this circuit.  How exactly does the charging circuit work and can I remove it completely?  I have to redo the zip memory, because I mixed up SC and PM zips, so I might as well take care of the battery issue too.  The battery area of the motherboard is clean.

[Kawazu]

[Kawazu]

I hope that will give you some light on the problem.

[Zac67]

+12V is just used to avoid the voltage drop from the inline diode in order to raise the charging voltage, no need to worry about.

[Castellen]

I would like to do the CR2032 coin battery install in my Amiga 3000T.  I was wondering if I could desolder and remove R192 and replace it with a 1N60 diode.

Yes, replacing R192 with a germanium or Schottky diode would work fine.  Obviously the anode side goes to battery + and cathode (stripe side) to U190 pin 18.  You won't need any other modifications than that when replacing the battery with a coin cell.

For a more detailed analysis of the entire battery and diode topic, read my posts in this recent thread.

[nscaleworld]

Why is R192 there, what does it do?  What parts make up the charging circuit and can they be removed?

[Damion]

I believe the resistor is there to control the charge rate of the original  NiCad. (The original charging circuit doesn't seem to have any means of detecting full-charge, but I don't know how important that is in this application.)  It's useless when replacing with a coin battery and diode. While leaving it in place does little harm (referring to Castellen's earlier comments), it's a handy place to install the diode, with the benefit of being able to easily solder the 2032 coin socket directly to the board, and potentially a bit longer battery life with a Germanium or (better) Schottky diode.