Date   : Sun, 19 Jul 2009 23:11:00 +0100
From   : philb@... (Phil Blundell)
Subject: FileStore battery

On Mon, 2009-07-20 at 09:32 +1200, Michael Foot wrote:
> With the diode and resistor, the reading is around 3.9V. I'm not sure if 
> that's within tolerence or not. I could change the resister to a larger rating 
> if need be.

Most likely it'll be fine.  I would guess that the battery is only
connected to the RTC chip (the schematics would confirm that) and those
ICs generally have quite a wide range of acceptable input voltages.  It
almost certainly runs off +5V when the machine is on mains power and I
would be fairly surprised if 3.9V or even 4.5V wasn't perfectly OK.  You
could check the datasheet for the chip in question to find out for sure.

> I really wish Acorn had not soldered Nicads onto the motherboards of all it's 
> machines. I have 40-50 machines here and it's taken me hours to open then all 
> up and remove the batteries! Some I've been too late to prevent damage but 
> mostly that damage was done by the time I got them. One A540 is too far gone I 
> think. Shame as they are very rare in N.Z.!

Yeah, I recently had to spend a tedious couple of hours repairing
battery damage on my A5000's motherboard.  It's quite impressive how
effective that gunge is at dissolving PCB tracks.  Luckily the A5000
doesn't have a great deal of circuitry near the battery, but if the
A540's is mounted in a more vulnerable area then I could well imagine
the motherboard would be scrap after a serious leak.

p.