How to Reset a Drain Capacitor for an HP 12C

by Blaze Johnson; Updated September 26, 2017

The HP 12c is a battery-powered programmable business calculator that features a small form factor, LCD display screen and includes over 120 financial related functions. Users have the ability to figure amortization, depreciation, cash flows and several other business related calculations with the HP 12c. If you ever experience errors, or if the HP 12c fails to power on, resetting the device may rectify the issue. Draining the internal capacitor may fix errors relating to unintentional static charge that affects the device’s circuitry.

Step 1

Remove the battery cover located on the backside of the calculator.

Step 2

Remove the small coin sized battery or batteries from calculator.

Step 3

Straighten a small paperclip in order to bridge the two metal battery contacts, located within the battery holder. If your particular calculator operates on one battery, use a penny to bridge the battery contacts.

Step 4

Bridge the battery contacts with the paper clip or penny for ten seconds. If your model uses one battery for operation, hold the “ON” key simultaneously for ten seconds, as well.

Step 5

Reinsert the battery or batteries and replace the rear cover.

Step 6

Press the “ON” button. The LCD screen will read “Pr Error” after a successful capacitor discharge. Press the “ON” button once more to clear the display and restore proper functionality. If the calculator fails to display “Pr Error," remove the battery or batteries for at least 24 hours to discharge the capacitor.

About the Author

In the spring of 2008, Blaze Johnson decided to share his expertise through writing. He studied business administration at a local community college and runs his own driveway mechanic service, specializing in computer-controlled vehicles and custom car audio installs. Johnson also serves as the de facto computer repair person for his family, friends and coworkers.