Hewlett-Packard HP-12C

Factory Reset Instructions

1. Press ON to turn off the calculator.
2. Press and hold [ - ] .
3. Press and release ON .
4. Release [ - ] .
5. The screen will display “Pr Error ”
6. The calculator will reset to the default settings, and the memory will be erased.

Resetting to drain the capacitor

If the calculator is still performing unexplained errors or will not turn on, it might have a static charge. This means the capacitor is full. The previous reset will not drain the capacitor. With this calculator, there are two options for draining the capacitor. The option to use is dependent upon the serial number of the calculator to be reset. The first option is a paperclip reset.

Paperclip reset

A paperclip reset can be performed on all HP 12C calculators with serial numbers before CN11500001. This will include serial numbers that start with numbers or with other letters. These calculators will have three 1.5 volt button cell batteries. Follow these steps for calculators in this serial number range:

1. Remove the battery door.
2. Take the batteries out.
3. Take a paper clip and bend it out enough to cross over from one terminal to the other.
4. Hold the paper clip across the battery terminals for approximately ten seconds.
5. Replace with a fresh set of batteries, being sure to follow the polarity assigned. Note the picture beside the battery cover.
6. Replace battery door.
7. Turn on the calculator. The display should read "Pr Error". Press and release the ON key twice.

Coin reset

A coin reset can be performed on all HP 12C calculators with serial numbers after CN11500001. These calculators will have one CR2032 battery.

1. Remove the battery door.
2. Tap the calculator gently into your palm to remove the battery.
3. Place a small battery-sized coin (penny or a dime US) flat into the battery compartment. Hold the coin in place with your finger.
4. While holding the coin, turn the calculator over, press the ON key, and hold for 10 seconds.
5. Remove the coin.
6. Replace the battery, being sure to follow the polarity assigned. Note the picture on the calculator.
7. Replace the battery door.
8. Turn on the calculator. The Display should read “Pr Error ”. Press and release ON twice.