Luis Loeff wrote:

> My first impulse would be to clean it with soup and water and a brush.

  Excellent idea.  *Then* use an air blast to remove most of the water,
followed by a hair dryer (not *too* hot), then the alcohol and
toothbrush, then dry again...

  If you see corrosion across a track, polish it with a pledget of
steel wool held in tweezers (then clean the PCB *again* afterwards at
least with a dry brush).  If this reveals a break clean across the
track, you have already removed the solder mask; carefully run solder
along the track.  If this will not bridge the gap, have someone hold a
scrap of Tinned Copper Wire (cut-off resistor lead) along the track and
solder that on.

  Dubious feed-throughs can have this wire inserted through, bent down
onto the track and soldered each side.  Longer lengths of rotten track
can be bridged with lengths of Wire-Wrap wire or for power traces,
telephone wire (solid conductor).

  *Fortunately*, board manufacturing quality is usually such that the
corrosion does not get *under* the track (other than by eating right
through) and for this reason does not usually damage the internal
connections of vias, or blind (rare) or hidden vias.  Most of the
circuitry near the battery/ keyboard connector on PCs old enough to use
Ni-Cds is sparse and does not use the internal planes, or can be seen
and thus bridged if necessary.

  Small amounts of damage can be cleaned repaired and if the battery is
removed (forever), the board will have a good life.  *All* boards with
Ni-Cds should be prophylactically treated by removal of the battery
immediately and its reconnection via at least 6 inches of insulated
miniature twin ("figure-8").  This can then be replaced as it degrades.
--
  Cheers,
        Paul B.