10 Mar
2011
10 Mar
'11
7:26 a.m.
This was a major design flaw in the Pole Position arcade PCB's, someone
positioned the backup battery at the top center of the board when it was
mounted sideways on the inside side wall of the cabinets and when the
batteries died, they died a horrific messy death, usually taking out a 3
square inch of the PCB traces with them.
Philip Pemberton wrote:
On 10/03/11 13:47, Mr Ian Primus wrote:
I've used CR2032's as replacements before
on similar machines, it's
worked fine.
Just remember - whatever you do, REMOVE the old soldered in battery
from the board. It'll leak and corrode through traces.
I'll second this with one addition -- the electrolyte in NiCd
batteries also eats some types of glass-fibre PCB substrate. What this
means is that you not only lose the tracks, but the board itself
basically turns to dust as well...
Get a pair of wire cutters (the "flush cutting" kind ideally) and cut
the thing off the board, then desolder the stubs and clean the PCB
with vinegar, then water (ideally deionised or distilled), then
isopropyl or a standard PCB cleaner / flux remover.
This works thusly:
1. The vinegar neutralises the alkaline electrolyte (usually
potassium hydroxide)
2. The water gets rid of the vinegar and any water-soluble dirt
3. The IPA removes any alcohol-soluble dirt (e.g. solder flux) and
helps the water evaporate more quickly.
I've
desoldered them and installed CR2032 sockets in their place with good
success. But if you don't want to go to the trouble, you can just
clip off the old battery.
Usually there's a 4-pin header which allows you to install an external
battery once you've removed the board-mounted one. These are usually
designed to take 4.5V alkaline batteries and generally have a diode
and series limiting resistor on the PCB.
The Acorn BBC Micro (actually the Master series) used three AAs in a
shrink-wrapped package shoved in the gap between the keyboard and the
case... IIRC there was a 120-ohm resistor and a 1N4001 diode inside
the package -- the resistor limits current if the diode fails.
Earlier machines had a battery holder by the side of the motherboard.
You could remove the old batteries and replace them with off-the-shelf
AAs. Unfortunately the battery holder sits in the Tube co-processor
bay, so you can't install an internal co-processor without replacing
the battery pack with the shrink-wrap version. There's nothing
stopping you installing an external cheese-wedge co-processor though...
(And with that tangent over and done with...!)