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HP Forum Archive 18

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How to clean the buttons on HP 48G?
Message #1 Posted by Denizen on 13 Jan 2009, 6:56 p.m.

I've heard that there's been posts here on ways to clean the buttons on the HP 48G's. I tried searching the forum, but no luck so far. Can someone point me to the posts?

Does it require taking the calculator apart? Or use compressed air cleaners? Thanks in advance.

Edited: 13 Jan 2009, 6:57 p.m.

Re: How to clean the buttons on HP 48G?
Message #2 Posted by Dallas Osborne on 14 Jan 2009, 1:28 p.m.,
in response to message #1 by Denizen

Sadly, the 48 series keyboard sandwich insides are impossible to clean and you can't take them apart without destroying them. Rebuilding your 48g with a working keyboard (a Dr. Frankenstein operation) is near black magic and requires another, working, 48g keyboard anyway. The keys themselves are one plastic piece attached by sprees that work as hinges. On the backside is a post that strikes a plastic dome of plastic. This dome is the front part of the sandwich. On the other side of the dome is a thin carbon button. When you press a key, the post dents the dome and the button strikes a contact point that closes a circuit registering a keystroke. This contact point/traceboard PCB is the middle part of the sandwich. On the back is a metal plate. Plastic heatstakes pin all of this together. If you cut the mushroomed heads off to open the sandwich, everything pops apart and it is effectively destroyed. (I have rebuilt a similar one (42s); the pioneer series uses the same keyboard design. It was nasty. It took multiple attempts. And I used tons of JB Weld and beer to accomplish the task. It actually worked for almost a year.)

Okay, the answer to your question: 1) If all the keys work just fine: (Take out the batteries.) Use compressed air and a soft toothbrush to remove as many bits and pieces as you can. Then use a squirt bottle or similar item to jet (moderate pressure) ethanol then D.I. water followed by ethanol between the keys to rinse out any bits and goo between them and the plastic domes. Hold the calculator at a reverse angle so you can get your solvent to drip out at the bottom of the keyboard rather than into the guts. Let it sit upside-down a good long while in a warm area (e.g., on a heater vent over night, in the oven at 50-ish degrees C for a few hours, NOT in the sun).

2) If the keys don't work - save the guts and LCD as spare parts for the replacement you will need to buy.

Good luck!

Re: How to clean the buttons on HP 48G?
Message #3 Posted by nacho on 15 Jan 2009, 6:12 a.m.,
in response to message #2 by Dallas Osborne

look at this:


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