New approach for repairing/resassembling HP Pioneer keyboards

[VIPQualityPost]

Hello everyone! Big fan of reading through the old forums, but first posting here.

I have found a methodology for repairing the HP Pioneer series keyboards (should be functional for other series, but have only tested on 42s so that is as far as I will guarantee ). While Mr. Brogg has contributed significantly to the repair guides for many of these calculators, his warning on removing the keyboard has always scared me away from doing it- and this guide will hopefully convince you otherwise (if you have any dead keys or row issues). This method is partially destructive, so I only recommend this if you're interested in actually using the calculator and restoring functionality. A final note: this doesn't fix any issue if your domes on the membrane are broken (the buttons don't have any resistance when you push them).

Basically, you should remove the main PCB as per usual, with undoing the twist tabs. After this, however, you can feel free to use a pair of flush-cut snips to get the many heat stakes off the metal shielding. Note, that with this approach, you do not need to remove the LCD or the 'zebra-stripes', saving you some effort. After removing the heat stakes, you can gently lift the metal shielding off, there is only glue holding it down near the display. Clean each of the layers of the keyboard gently with a cloth or something, and check for any stray material bridging the contacts (this was the issue on mine, sometimes the conductive material can begin to flake with age). Now, the difficult part seems to be re-assembling the keyboard. Stack the membranes with the shield back now that they are cleaned. To fully tighten the membranes against the keypad, use some 1/16" heatshrink- slide it over the posts that used to hold the heat stakes, while cold, and cut the tops about 1/4" (~1cm) above the metal shielding. After they are all assembled, shrink them with a heat gun- the friction will hold them very tightly. Now, take a hot solder tip or woodburning tool, and flatten the excess rubber while holding or clamping the plate down so there is very little play. If you do it correctly, there will be no play when all of the stakes are melted and pressed against the metal shielding. This is basically just a method to replace the original heat stakes. If there is any play, you will probably get a row of dead keys, rather than a single key- that is OK, it is fairly easy to open up the calculator and try again. It is key to make sure that the membranes and the metal shielding are as tight as possible against the front of the housing. The rubber of the heatshrink is very forgiving, and will let you rework it 4-5 times before it starts to burn.

Hopefully this helps at least one other person to restore their calculator! I was very happy when mine passed the self-test for the first time in years.

Cheers,

Matei Jordache

[Dave Britten]

Very clever idea. I've always replaced the tops of the stakes using a hot glue gun and some pressure to hold down the plate while the glue sets. It's not totally perfect, but the results are pretty good.

Yesterday, I fixed a couple of broken key hinges/legs using JB Weld Plastic Bonder. It got me thinking that this might also be a good heat stake repair compound. It takes a lot longer to set/cure than a glue gun, though, so you'd have to leave it clamped quite a bit longer.