After switching the 3 AAA batteries of my beloved HP 48G calculator, it didn’t turn anymore when hitting the “ON” button in the bottom left corner. I first thought it’s because of poor electrical contact due to poor QA batteries (I noticed the new ones were a fraction of a mm shorter than the previous ones). This might have played a rule in the sudden failure to power on my HP 48G, but it probably wasn’t the only reason.
Here are some “tricks” to try, if your HP 48 won’t turn on:
- Double-check that you inserted the AAA batteries pointing with their (+) poles in the right direction (left, right, left)
- If the AAA batteries have poor electric contact (particularly the middle one is susceptible to this), cut out and fold some aluminium foil (also called “aluminum foil”; historically “tin foil” was used), and put it where better electric contact to the batteries is needed.
- Press the “ON” button in the bottom left corner
- If that doesn’t work: press and hold “ON”, press and release the “C” button, release the “ON” button
- If that doesn’t work (it didn’t for me): Press the area between the “B” and “C” buttons/keys, then press and release “ON”
- If that still doesn’t work (it didn’t for me): Flip the HP 48 over and remove the upper right rubber foot. You can basically just wiggle it a bit and pop it off, there’s no need for special instruments. Underneath, there’s a little hole to reset the calculator. Use e.g. a paperclip, insert one end into the hole until you hear or feel a subtle “click” sound to reset the calculator (please bear in mind that this could also clear the memory).
Then press the “ON” button and you’ll be prompted to try recovering the memory, which you should confirm. - At this point, unless it’s a severe error of the board, your HP 48 should turn on again.
It might display “Warning: Invalid Card Data” at every start though. You can get rid of this warning message by typing “PINIT” (without double quotes) and pressing the ENTER button (source: https://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv013.cgi?read=43990)
If none of the above tips help, your HP 48 probably needs repairing.
It seems to be quite a nightmare to service the HP 48, but there are a couple of videos out there of people repairing a HP 48 SX (disclaimer: know what you’re doing, follow at your own risk):