Repairing

  Keyboard problems normally fall into three categories.  First being stuck or missing keys (ie key presses don't register). Second the "Num Lock", "Caps Lock", etc don't light up.  Or the dreaded, "Keyboard not found", sometimes 
visible or the system is intelligent enough to assume it's operating
headless.

  If the problem relates to the first and not the second as well,  The 
problem refers to dust or other impurities getting between the contacts.  Most keyboards built within the last 15 years rely on a rubberized pad that
is pressed against the circuit board completing a connection.  Often little
Bill or Steve has dumped, coffee or slurpee into the keyboard.  The solution
involves taking apart the keyboard and gently cleaning out any dust or caked
on coffee or slurpee.  The safest solution I have found is water, using a 
damp and not dripping cloth, gently clean off any visible contaminants.  Then
allow the component to dry for at least a day or two before re-assembling.
Test again, if the problem persists try cleaning again or replace.

  If you're keys with LED's don't light up (do they work but not light up?), 
the problem could be a dead LED.  Either learn to deal without, or get your soldiering iron and start replacing (watch your LED anode & cathode).

  Lastly, the keyboard may have a damaged cable or circuit board, the
problem is normally a break or short in the cable.  For those who are 
adventurous, or can't afford to replace, now is the time to break out the
multimeter.  With the multimeter, you will be needing to test continuity
of the tail. Often this is challenging because the colour codes don't reflect any specific pin locations.  Record the pin numbers and colour codes for
later.  At this point if it's only 1 broken wire, with an assistant ask them
to slowly start flexing the wire in 1 to 2" lengths, when you suddenly have 
continuity you've found the damaged section.  In the best case you will 
simply be shortening the cable length to bypass this point, otherwise you 
will need to wire up a new cable to completely replace the old one.
  If you find that no wires are broken, you will most likely need to replace.
As the problem in that case relates to a damaged circuit board or chip.


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Article by Slam, Last Updated June 2004