If necessary, examine all of the 4 sets of connectors pictured, especially the 6 pin molex. It may have connectors inside the plastic that have expanded with time/heat/fatigue.
Typically Fault/Error/No Voltage/Low Voltage is a wiring connection.. Check the power receptacle first. Then unplug the power and remove the four screws to the control panel. Check the control panel connections to the interface board. Unplug and replug both ends of the grey ribbon cable from the interface board to the keypad panel, and from the interface board to the main board. Retest with power.