Mostly Non-Destructive HP-48 Series Keyboard Fix

[Anthony L. Mach]

Hello Everyone:

After picking up one of the many basket case HP-48G units on TAS, I decided to take a crack at fixing one that "didn't turn on." Many of you know that this is a consequence of the keyboard ribbon cable not making contact with the board. The quick fixes just don't work that well when you have to press on two spots to get anything to work!

This unit was in excellent condition and purchased shipped for $18 USD. So, why not? The options have been limited - generally either ripping the faceplate off and removing the heads off of the rivets, or trying your luck at "pop the case." This one was of Singapore manufacture. Either way, I wasn't going to wreck this one if I could help it.

Anyway, here's what I did (usual disclaimers apply):

Obtain a zip tie that is 1/8" wide or less by at least 4" long (sorry about the imperial measure). If you can find a zip tie that is on the thinner side, try it first. The 1/8" one just fit, but was tight. Using a flush cutter, start splitting the pointed end of the zip tie down the middle. Cut in about 1/2". Cut off one of the ends. The goal is to create a pointed end that slips easily above the ribbon cable. Again, if you can get a thin zip tie, try it without cutting it. Keep the ribbed end facing away from the ribbon cable.

   

Using a toenail clipper handle, insert gently near the top row of keys on the lefthand side. Go in just next to the menu key labeled A. Pry up gently.

   

Locate the ribbon cable. It's white, but extremely tough to see. Work the zip tie above the ribbon cable and just to the right of the block that holds the ribbon cable. Insert far enough to make reasonable contact and test the keyboard. Test every key, especially the menu keys! Once you tuck the zip tie into the case, it's not easy to get out (trust me).

   

I had to go in the whole width of the ribbon cable before the righthand keys were operable. I then pulled the zip tie back out a bit, cut with the flush cutter, and pushed it inside the cover with a small flat-headed screwdriver.

   

Pull out the toe nail clipper blade. Push the case together lightly. Success!

Good luck!
73,
Tony, AB9IO

[Jamieson]

Hi Tony,

Thanks for documenting this interesting take on fixing that darn keyboard flex cable to main board connection. I tried this but wasn't having any luck positioning the plastic under the flex cable. So I went the usual route and fully opened my HP48G up, removed the PCB and replaced the gummy nasty evil foam spacer under the flex cable.

[EugeneNine]

Wish I had thought of this before taking mine apart.

I bought another non working from ebay so I can build one working from two non after messing up the front of mine.

What are you replacing the foam with, I've been looking through digi-key, mouser, etc trying to find some foam tape that small.

[adumont]

(09-12-2018 01:32 AM)EugeneNine Wrote:  Wish I had thought of this before taking mine apart.

I bought another non working from ebay so I can build one working from two non after messing up the front of mine.

What are you replacing the foam with, I've been looking through digi-key, mouser, etc trying to find some foam tape that small.

From what I understand, he leaves the zip tie in there that will pressure the ribbon cable onto the connectors below. I have hard time figuring out how to/where to put the zip tie... maybe a diagram would help. I have been watching countless videos to understand the inside of the HP48, but still. Also with the small opening, I don't really understand how we can position the zip tie in the right place. I guess it a matter of trial and error... I have nothing to loose anyway, so I guess I'll trie that at some point.

[EugeneNine]

Well, this is an old thread, I've learned a lot since then. Get a bottle of isopropyl alcohol and cotton balls. take out the batteries and remove the doors of the calculator. Soak some cotton balls int eh pa and squeeze them out on the keyboard overlay. Let sit for a few hours and apply more if needed. The ipa will dissolve the glue and the thin metal overlay will just come right off without bending. If a part of it doesn't want to come off then stop and dribble some more ipa in. Once the overlay is off you can get to the rivets that hold the top and bottom together easily.

[gwh]

(01-29-2023 05:37 PM)EugeneNine Wrote:  Well, this is an old thread, I've learned a lot since then. Get a bottle of isopropyl alcohol and cotton balls. take out the batteries and remove the doors of the calculator. Soak some cotton balls int eh pa and squeeze them out on the keyboard overlay. Let sit for a few hours and apply more if needed. The ipa will dissolve the glue and the thin metal overlay will just come right off without bending. If a part of it doesn't want to come off then stop and dribble some more ipa in. Once the overlay is off you can get to the rivets that hold the top and bottom together easily.

There's a much better, non-destructive way of opening it: https://www.hpcalc.org/details/4701 and https://www.hpcalc.org/details/3417

I've opened 2 SX and a GX like this and while I haven't yet fixed them yet (faulty keyboard and/or screen connections), I'm pretty sure I can close them and no one would be able to tell they've been opened.

[EugeneNine]

What I'm describing is non-destructive also. You soften the glue holding the metal keyboard labels so you can take it off and then glue it back on when complete.