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Suggestions for an HP48 keyboard repair?
09-15-2019, 12:54 AM
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Suggestions for an HP48 keyboard repair?
Hi everyone,

I have a question regarding the repair of an HP48 keyboard. I managed to pick up an HP48GX for under $50 from TAS recently that was advertised as not working. I had hoped that it suffered from the usual problem of a deteriorated keyboard "sponge" and would be easy to fix. Unfortunately that was not the case so suspicion fell on either a bad CPU board or a bad ON key not waking the processor. To test the CPU board I swapped it into a 48SX I had opened while working on a homemade 128K RAM card. You can see the result of the test here.

[Image: uc?export=view&id=1sBtUo_YrzQuza...wmrWxkTYTU]

So the CPU board is fine but while trying to replace the "sponge" on the original 48GX keyboard I managed to tear the flexible connector contact material at one of the contact strips. I checked continuity for the connection and it looks like it is broken. The end result of course would be the loss of a row or column of keys. I might be able to put tape or layer of cement on the back of the connector to immobilize the two sides of the tear, but I'm unsure what I might use to electrically connect the two parts of the strip. Any suggestions?

On the other hand, the 48SX body does have a black LCD transplant which looks pretty nice. Perhaps having swapped the CPU board I should finish the job by swapping the lower part of the faceplate, keeping the nice molded logo at the top. That would certainly cause a double-take for anyone seeing the calculator. Any hands up for that approach to recovering the 48GX? For background, this is only the second GX I've managed to acquire, but I already have several SX models I picked up quite cheaply, advertised as not working. I definitely want a second working 48GX!


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Suggestions for an HP48 keyboard repair? - mfleming - 09-15-2019 12:54 AM

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