Re: HP-42S faulty keys Message #11 Posted by robert rozee on 24 Apr 2009, 12:34 p.m., in response to message #1 by wesjones
i worked on a 42s for a friend a while back, and as i recall the contact between the keyboard matrix and the 'motherboard' is purely by pressure, through a dozen or so contacts in a row. i'd guess that the failure is here, and that cleaning may well fix the problem.
to dismantle, the best method i've found is to drill out the 4 (?) plastic rivets in the battery compartment area, and through the back of the calculator to disconnect the 4 (?) at the bottom edge - after some careful measuring to work out where you want to drill.
once the back is off, you can easily remove the motherboard and clean the connections between it and the keyboard, before reassembling it back into place. the only repair work then required will be reattaching the back. oh, and while it's apart, you could upgrade the ram from 8k to 32k.
cheers,
rob :-)
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