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Suggestions for an HP48 keyboard repair?
09-15-2019, 12:54 AM
Post: #1
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!

~Mark

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09-15-2019, 07:41 AM
Post: #2
RE: Suggestions for an HP48 keyboard repair?
Hi,

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

https://www.amazon.de/Silber-Leitlack-St...B00LTWQWXW

Michael
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09-15-2019, 05:40 PM (This post was last modified: 09-15-2019 05:42 PM by mfleming.)
Post: #3
RE: Suggestions for an HP48 keyboard repair?
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.

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09-16-2019, 01:42 PM
Post: #4
RE: Suggestions for an HP48 keyboard repair?
Hi,

hope I understood your question. Look at https://www.instructables.com/id/USB48G-...-Keyboard/ Step 3: Correspondence Table
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09-17-2019, 02:25 AM
Post: #5
RE: Suggestions for an HP48 keyboard repair?
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

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