HP48S strange behavior

[BartDB]

Hi Daniel,

It could be that the battery leakage has got onto the electronics or worse into the keyboard.

Attached is a PDF of Han Duong's opening the HP-48 guide.

  Opening the HP48.pdf (Size: 905.23 KB / Downloads: 20)

However, he uses a blunt metal tool, I usually use a plastic tool found in mobile phone repair kits:
Although they are prone to breaking I find they do less damage.
   

Once open, you'll have to undo the twist tabs to remove the PCB from the keyboard - the screen can be removed as well.

Check & clean the PCB. If the keyboard needs cleaning I suggest you not take it further apart as the plastic rivets are almost impossible to restore/replace. Instead I suggest you try the "wash and dry" procedure described by Geoff Quickfall (for a different calculator, but the principle is the same) in message #15 of this thread: https://www.hpmuseum.org/cgi-sys/cgiwrap...694#175788

As you have the calculator open, I suggest you replace the connector sponge. Just below the screen you will see the keyboard connector flex-pcb.
   
Underneath is a grey sponge strip that pushes it onto the main PCB. This sponge deteriorates and causes a bad connection. It is best to replace the sponge strip it while you can.

When re-attaching the PCB, the twist tabs have to be done up securely to prevent missing lines on the LCD (make sure the zebra strips and connections are squeaky clean). (doing this I always sweat a bit - the balance between doing it tightly and not breaking the tabs)
.