OKI MB770

LCD does not display anything.

Check item	Check work	Action at NG
Check CU board		Replace CU board.
Check the system connection
Connection between the low voltage power supply unit and the CU board.	Check if the cable from the low voltage power supply to the POWER connector ⑦ of the CU board is normally connected or not. Check if the connector is connected only in the half-way or not, and check if the connector is inserted in slanted angle or not.	Re-connect the cable normally.
Cable assembly connecting the low voltage power supply unit and the CU/PU board.	Check if the cable is half-open circuit. Check if sheath of the cable has not peeled off or not. Check if the cable assembly is defective such as internal wires are disconnected or not.	Replace the cable with the normal cable.
Connection between the CU board and Operator Panel	Check if the cable is connected to the OPE connector (34) of the CU board normally or not. Check if the connector is connected in the halfway only or not, and check if the connector is inserted in a slanted angle or not.	Re-connect the cable normally.
Connecting the CU board and the Operator Panel board	Check if the cable has open circuit or not with VOM. Check if sheath of the cable has not peeled off or not by visual inspection.	Replace the OPE unit
Check the peripherals of the power supplies
Primary AC power source that is connected to the printer.	Check the supplied voltage of the AC power source.	Supply the AC power.
5V power that is supplied to the CU/ PU board.	Check for the 5V power supply at PU ⑦ :Pin-11,13 CU ⑦ :Pin-1,2,3 of the POWER connector of the CU/PU board.	Replace the low voltage power supply.
Check that power supply circuit has no short-circuit.
5V power and 24V power that are supplied to the CU/ PU board.	Check that power supply circuit has no shortcircuit at the POWER connector ⑦ of the CU board. The follow voltage must appear respectively.PU ⑦ Pin 1,2,3,4:24V Pin 5,6,7,8:0VP Pin 9,10:0VL Pin 11,13:5V CU ⑦ Pin 1,2,3:5V Pin 4,5,6:0VL Pin 10,11:0VP Pin 12,13:24V If any voltage does not appear and short-circuit is detected, locate the source of the short-circuit as follows: Disconnect the cables that are connected to the CU board one cable after another until location of the short-circuit is found out.	Replace the part causing shortcircuit.

Error messages related to Operator Panel are displayed.

Check item	Check work	Action at NG
Error message	Check the error contents by referring to the Error Message List.	Follow the instruction.