WARNING: The following procedure must be done by a qualified service technician only after the unit has been disconnected from mains power.

1. Turn the unit off and unplug the unit from mains source power.
2. Remove the top cover from the unit.
3. Disconnect the cable from the keypad assembly.
4. Remove four nuts and washers to remove the keypad assembly from the chassis.
5. Separate the rubber keypad from the printed circuit board. Some models have four spacers between the rubber keypad and the printed circuit board. These must be saved for reassembly.
6. Using a Q-tip and denatured alcohol, clean the printed circuit board contacts.
7. Reverse the preceding steps to reassemble the unit, taking care to reinsert spacers if noted during disassembly.