HP-48's display with an unusual(?) stain

[vaklaff]

(09-26-2023 08:14 AM)vaklaff Wrote:  Thanks for all the replies. Looks like there’s no other way than to open the machine and start from there. If I manage not to break it for good, of course :-) Wish me luck!

Is Han’s Opening the HP48 the current state of art? I managed to open and fix a Pioneer but this thing is a completely new level…

TL;DR: I was lucky and replaced the rotting display.

Details:

I went through the document and watched HP 48G+ gets repaired!. (Many thanks to the authors if they read this!). I decided to use wooden sticks from the best ice cream bar ever made as the prying tools, I thought they would unlikely leave dents.

Opening went rather well, except for the bottom part where I lost patience and just tear the calculator apart. Fortunately not much damage done, I just broke a few of the rivets keeping the keyboard and metal frame together.

First of all I "fixed" the connection between the keyboard and the PCB: just added a thin foam strip on top of the original rubber strip. It looked already deformed and aging. I hope the added strip will postpone the usual keyboard problems I saw on some 48 machines.

Then I replaced the display with a HP40's one. I spent more than an hour on aligning the display, the conductive strips and the PCB. That was the most frustrating part. The display and the strips have too much free space around and you have no clue if they are all aligned correctly. It's just trial and error. Fortunately there was a happy end after all, the new display caught up.

The fixed GX next to a G+ which has the same display the GX had: https://i.imgur.com/PovYkbr.jpeg
The idea was to get rid of the display rot in the GX but getting a much better display is indeed a nice bonus :-)

Looks like the few broken rivets aren't that much of a problem, the keyboard passes the self-test and feels normal and uniform.

Just for fun I tried to get to the blemish ("rot") in the old display but didn't succeed. The layers stick together too firmly.

Lessons learned:

• Have patience when opening a 48, follow Han's document to the letter.
• Even more patience is needed when positioning the new display. Try and try again.
• Always have a few ice cream bars around, they can be of great help!
• I'm not going to put a black LCD into my pristine SX. Too risky and too much effort just to have the best looking of all calculators. I'm not sure it's true anyway ;-)
  

Edit: typos