BACK TO DIAGNOSTICS
a. Open lines
Refer to the drive and sense diagram
for your model.
Connect an ohmmeter to the appropriate drive and sense lines for the affected
key(s).
Depress the key. It should read less than 100 ohms.
b. Separating
Inspect the bottom of the keyboard for
broken welds. A few may not be a problem, but if
there are several in the same area, it is a likely cause. Try to pry a few
adjacent welds. If
they fall away easily, they were’nt doing any good anyway. Temporary
gluing, screwing,
etc., will only make matters worse.
c. Spill
The simplest way to confirm this diagnostic
is to get the customer to ‘fess up. If you’re
reluctant to make an accusation, look closely at the side edges of the cap
base. Most
spills seep in along the edge. Carefully lift the black rubber membrane
to expose the
traces for discoloration or other evidence of spill residue. If you can’t
see it, smell it
(gross, but effective). Inspect the bottom of the base plate. Spills often
seep through the
plastic welds or along the bottom edge.
d. Bad keysprings
If it doesn’t click, it doesn’t
work. With power off, listen closely for a sharp click on the
down-stroke and a slighter quieter up-click. Try known good keys for comparison.
This
is often corrected by simply reinstalling the keycap. Remove the keycap
by prying up
from the front of the cap. Tip the machine or hold the keyboard so that
the connectors
are pointing down and the keyspring falls to the back of the chimney. Push
the cap back
on and test. Try a different keycap. If the problem persists, replace the
spring. Twist it
anti-clockwise while pulling up gently. Using a bristol or allen wrench
that just fits
inside the new spring, place it on the mounting node of the keyswitch rocker.
Place the
forked end of a spring hook near the base of the spring and nudge it into
place. Reinstall
the keycap and test. This may take a few tries, but if you’ve given
up by now you’ve
made a good decision. Send it in.
Attempts to repair typewriter keyboards may cause further damage.
Plesase call tech support before proceeding.