Re: Halfnut dissasembly question Message #5 Posted by Jerry Ballard on 3 Mar 2001, 11:19 a.m., in response to message #4 by Ion Abraham (New Mexico USA)
I took apart an HP41-CX Halfnut with very bad sticky keys. I found that the board that has the key contact circuit is attached to the top case part by plastic stubs or pins (total of 36) that are molded into the plastic top case. The key contact printed circuit board (PCB) is placed over the keys onto the plastic stubs, then the plastic stubs are melted down to attach the PCB. The four metal tabs at the top only hold the display LCD onto the key contact PCB. I carefully cut the plastic stubs off to remove the key contact PCB. I was able to clean the contacts, but now the plastic stubs are not long enough to reattach the key contact PCB. I found some very small screws but I am not sure they will work.
The moral to this long story is that I would not try to get to the key contacts directly or you will have an HP41 like mine that is a box of parts. Keep trying the compressed air or some recommended contact cleaner.
If you use contact cleaner, you will need to spray a small amount into the feedthrough holes on the back of the key contact PCB. The center of each key contact has a plated feedthrough hole in the PCB. Then press the key to make some cleaning action. Hope this helps.
Using the compressed air or contact cleaner from the top next to the keys will not help. Between the keys and the key contact PCB is a rubber insulator about 1/16-1/8 inch thick. Also, each key contact has a metal dome over contact area which is attached to the PCB with a large piece of tape.
If anyone else has experience in removing the key contact PCB and reattaching with success please comment.
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