Ricoh A151 Field Service Manual page 240

Check the voltage at CN114-6 on the main board.
0 volts 24 volts
Replace the main board.
Check the voltage at CN114-4 on the main board.
0 volts 24 volts
Replace the main board.
Check the voltage at CN114-8 on the main board.
24 volts 0 volts
Replace the main board.
Replace the ac drive board.
A151/A152 6-46 FSM