I recently purchased a really clean HP-25 at a church rummage sale. It came with an 82041A charger, a carrying case, a Quick Reference Guide, an Owner's Handbook and an Applications Programs book, but no battery pack - all for under a dollar. I charged a battery pack in my inventory and demonstratd that it worked by inserting it into an HP-27. It wouldn't work in my HP-25 until I cleaned the battery pack contacts in the machine. Once I got the HP-25 to turn on with the battery pack in place I connected the charger and proceeded to check out the machine.
The HP-25 comes on OK. I can change display modes, write programs, and enter numbers from the keyboard. I can STO and RCL. But doing any mathematical functions from the keyboard or in a program, even the decimal point, end up with 0.000000000 in the display and a changed display mode. I have tried twisting the case but that didn't help. Since the battery pack contacts were bad I suppose that it is possible that the previous owner had connected the charger and fried something. Are the characteristics I describe consistent with something being fried?, Is there a chance that I can so some good by opening the unit? I am not an expert solderer. Any ideas?