Re: Apple IIe keyboard repair

[dalloff@freenet.columbus.oh.us (Dave Althoff)]

Mart�n & Martorell (a.martin@tip.nl) wrote:
: 	The keyboard of one of our Apple IIe insists on repeating the last
: character entered indefinitely. Does anyone know which is the cause and/or
: how can it be fixed?

: 	We guess it is due to a burned resistor responsible for the determination
: of the keyboard scanning time constant, but the keyboard components are
: placed between the printed board and the keys themselves, is very difficult
: to access (unsolding tens of welded connections) and we miss any technical
: information about the circuit which might help us in locating the faulty
: resistor.

: 	Any assistance concerning this problem would be more than welcome and
: appreciated!

The very first thing you should do is remove the top case from the
computer.  Not the lid; the entire top case.  If your keyboard is attached
to the upper case (I am guessing your keybaord is attached to a couple of
supports attached to the lower pan, as one of mine is), then remove it
from the case.  Once you have done this, power up the machine and see if
you still have keyboard problems.

The "last-key-repeat" problem is a classic symptom of a STUCK KEY.  A
common cause for a stuck key, particularly if the machine has been
disassembled recently, is a slight misalignment of the keyboard with the
upper case.  The usual culprit is the "~" key.

If removing the keyboard from the case does not solve the problem, then
check eack key and find the one that is stuck.  The easiest way to do this
is to disconnect the keyboard from the computer and check eack keyswitch
with a resistance meter or continuity checker.  If you have the
older-style ][e with the keyboard attached to the base pan, you can mount
the keyboard upside down (keys facing downward) to the support legs for
easier access to the keyswitch contacts.  Just check each contact pair;
none should show continuity...but I will bet that one of them does.  When
you find it, remove the keycap and pull out on the switch stem.  Then
power up the machine and see if the problem has gone away.

To replace the keyswitch, which is the second most likely operation you
will need to perform, remove the solder from the posts on the bottom of
the keyswitch, squeeze the two locking tabs together on the top of the
switch, and pull it straight out.  Once the bad switch is out, you can
reconnect and test the keyboard to verify that it fixed the repeating key
problem.

Good luck; let us know what you find out!

--Dave Althoff, ][.
-- 
    /^\        _       _             ***  Still open weekends!!!  ***
   /XXX\      /X\     /X\_      _     /X\__      _     _        _____  
  /XXXXX\    /XXX\  _/XXXX\_   /X\   /XXXXX\    /X\   /X\      /XXXXX
_/XXXXXXX\__/XXXXX\/XXXXXXXX\_/XXX\_/XXXXXXX\__/XXX\_/XXX\_/\_/XXXXXX