I got an HP-33C that was in terrible shape; there was major corrosion damage to much of the internal components, and not much was salvagable. I also got an HP-38E that was totally non-functional, but looked OK inside. Both calculators were the type where the chips were not soldered to the circuit board, but were held in place by a backbone.
I took the 2 main chips (probably ACT and RAM) from the HP-33C and transplanted them to the curcuit board of the HP-38E. I then put the boards into the case of the HP-33C. Now the calculator always says "Pr Error" when I power it up, but it otherwise works perfectly. Functionally, it is the equivalent of an HP-33E!
Is there anything I can do to have the calculator save its memory when I power it down, such as adding or replacing a capacitor? Thanks!