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Joined: Oct 2008
Fix that calc.com might be able to repair. At the cost of Hp15c's it might even be worth it (though that paticular 15c may not except out of a perverse pride).
Older 12c's should work for a keypad donor.
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First problem is the WD40... Wanton Destruction 40 is a wax... it will gum up just about anything it touches including key switches.
Your best bet is to open up the machine and clean each key switch contact. Make a small wire brush out of three bristles inserted into a pin vise, twist together, and trim the end square with cutters. Under each key is a breather hole. Place a drop of 91% isopropyl alcohol on a hole, dip the brush in more alcohol, and the "scritch" around in the hole with the brush. Be careful not to break a bristle off in the hole. You will probably have to rebuild the brush every few holes.
If it were mine I would first run the machine through three cleaning cycles of an ultrsonic cleaner. Use distilled water and change it each time. Shake the unit as dry as possible between each cycle. Finally dry it for around 24 hours in an oven on low (<140 degrees). This technique does have the potential of damaging the machine, but it has worked wonders on some really bad cases.