Casio calculator problem

Seems to be a common problem on this otherwise great calculator that helped me through both high school and university. I've had mine for nearly 20 years and this problem showed up a few years ago. But I remember classmates reported the same problem when it was almost new.

If replacing batteries isn't helping, the problem is most likely caused by oxidation on the springs connecting the battery holder to the main PCB. The solution is as follows:

1. Remove the metal back cover (2 screws)
2. Remove the plastic back lid by removing the black screws (leave the batteries mounted) and CAREFULLY slide the back lid to the lower end (where the EXE button is located). Do not lift while sliding until the lid easily comes off.
3. On the back side of the plastic lid, very carefully bend the the two metal connectors ~1 mm on both batteryholders to increase their tension.
4. Clean the connecting pads on the PCB and the metal springs with de-oxidizer solvent.
5. Re-assemble and your 4500P calculator should be good as new.

Meter the batteries. It is likely you installed low batteries.