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Suggestions for an HP48 keyboard repair? - Printable Version

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

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!


RE: Suggestions for an HP48 keyboard repair? - mipa83 - 09-15-2019 07:41 AM


I heard that Silver Conductive Paint Pen could work for fixing wiring... but I haven't tested it ever....



RE: Suggestions for an HP48 keyboard repair? - mfleming - 09-15-2019 05:40 PM

This sounds like an approach worth trying. Depending on what the carrier/binding material is for the conductive silver, it might serve to hold the torn halves together. I also considered taking the faceplate from a 48g, but present TAS offerings are more than I paid for the GX!

Edit: Does anyone know what the row/column assignments are for the connector? Still need to verify the On key works.

RE: Suggestions for an HP48 keyboard repair? - mipa83 - 09-16-2019 01:42 PM


hope I understood your question. Look at https://www.instructables.com/id/USB48G-Upcycle-Broken-Hp48-Keyboard/ Step 3: Correspondence Table

RE: Suggestions for an HP48 keyboard repair? - mfleming - 09-17-2019 02:25 AM

Yes! That's it! Unfortunately testing shows the On key is not closing as it should, so the calculator is never awakened. Looks like the keyboard is a loss, but I'm getting oddly fond of a 48GX in a 48SX skin, particularly the color scheme. Maybe I'll keep it Smile