Re: How to fix vintage 12C enter key? Message #4 Posted by Jeff O. on 7 Sept 2010, 8:36 a.m., in response to message #3 by Peter Matthews
The following is from memory from disassembling an 11C a few years ago.
You should be able to unwrap or unfold the plastic wrapping to expose the back side of the keyboard printed circuit board, i.e., no cutting should be necessary. It may be necessary to peel off an adhesive edge on the plastic, I do not really recall. With the back off and plastic out of the way, the rest of the calculator (keyboard pcb, key contacts and top half of the calculator shell) is held together by about 40 plastic pins, known as heat stakes. The top of each of these pins is mushroomed over the keyboard pcb to hold the “sandwich” together. So further disassembly requires these heat stakes to be removed. Do not just slice the head off of each stake, instead carefully trim just the mushroomed portion off of each stake, leaving the center of the post sticking through the pcb. Once they are all trimmed, the keyboard pcb should come off. The key contacts consist of a sheet of metal domes, my guess is that the dome for the enter key is collapsed. I do not know if it will be possible to repair a bad dome, you might need a new sheet of contacts from a donor unit. If you succeed in repairing/replacing the contact, then you get to the hard part: reassembling the keyboard “sandwich.” You must hold the “sandwich” tightly together while either melting over the remaining portion of each heat stake or gluing each stake with your choice of adhesive. I believe someone here once reported building some sort of jig to hold the sandwich together while gluing or melting the stakes, but I do not recall who or if they reported total success.
I am not really a repair expert and like I said, the above is from memory. So, while I believe the information to be accurate, follow at your own (or your 12C’s) risk.
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