Classic Calculator dont turns on with battery

[AndiGer]

Check with an ohmmeter with no battery installed you get contact
a) from lower battery contact (plus) to left and right charger plug pins
b) from upper battery contact (minus) to center charger plug pin
If you don't get mentioned contacts you have to examine the reason.

If contact a) is missing you can try to get it work from outside without opening the calculator. Try to clean (or even bend a little bit) the gold plate that bridges the both outer contacts.