Lithium battery hack: 2 x AAA instead of coin battery?

[Castellen]

The RP5C01A real time clock has two modes of operation:
Operating and backup.

With a supply voltage of 5.5-4.7V it's in operating mode, draws significantly more current (250µA) and can be communicated with via the address/data bus.

If the supply voltage falls below 4.7V, it switches to low current (15µA) backup mode, where only the crystal oscillator and an internal counter runs in order to keep the time/date.

So to answer your question, the battery voltage at the RTC input (pin 18) must be between 4.7V and 2.2V for it to run in backup mode and without loosing data.


An easy solution for you would be to use 3 x Ni-Cd or Ni-MH cells in series.  Either AAA, AA or whatever.  That will give you a nominal terminal voltage of 1.2 x 3 = 3.6V.
This is exactly what's in most cordless phones.  The batteries are rechargable, so no modifications to the board are necessary.

I've written a guide for replacing batteries as well as using alternativcordless phone battery types:

http://amiga.serveftp.net/battery.html

[Castellen]

@dnelsonfl:
From the limited detail in the pictures, the damage doesn't look too bad.  Or you've made a really good job of cleaning it :-)

The address latch, U177, is often the cause of the system failing to see the RTC.  There are also tracks and vias under U177 which can get corroded open circuit.
I've written a full fault finding and repair guide here:
http://amiga.serveftp.net/hardware_repair.html

All you really need is someone who can carry out some SMD soldering for you.  The continuity measurements you can probably make yourself.  I get the impression you're a little more electronically skilled than the average joe :-P


@orange:
As mentioned already, the trimmer capacitor is used to fine tune the 32.768kHz crystal oscillator in the Commodore factory as the crystals used aren't overly accurite.  I think they're 20ppm or less stability, from memory.
The frequency also drifts as the crystal ages.
The best way to adjust the oscillator is by using a frequency counter or decent oscilloscope.  It only takes a few seconds to do with the correct equipment.

[Castellen]

That ChipQuick site doesn't seem to be working for me.
All you really need is to be able to remove the device (U177), which is simple enough.
It's a fairly large pitch, so you can easily get away with hand soldering on a new one.
I've also written guides on SMD soldering, you might find this one in particular to be of use:
http://amiga.serveftp.net/Replace_SOIC.html