Troubleshooting The +3.3 Vdc And (2) +5 Vdc Low-Voltage Power Supplies; Troubleshooting The 24 Vdc Lvps - Xerox 7750DXF - Phaser Color Laser Printer Service Manual

Troubleshooting the +3.3 VDC and (2) +5 VDC Low-
Voltage Power Supplies
Note
Switch off power and disconnect the power cord.
Actions
1.
Remove the rear cover and rear shield.
2.
Disconnect the harnesses to connectors P505, P510, P511 and 2nd BTR on the
T1 HVPS, remove 3 screws and lower the T1 HVPS.
3. Connect AC Power and switch the printer ON.
4. Check for proper AC voltage at the connector at the bottom of each LVPS.
5. If not present, go to the Troubleshooting AC Power section (link).
6.
Check for 3.3 VDC or 5 VDC at the connector at the top of the LVPS.
7.
If correct voltage is not present, unplug the top connector and retest. If no
voltage is present replace the LVPS. If the voltage returns check the harness,
image processor board, engine board, and relay board for shorts.

Troubleshooting the 24 VDC LVPS

Note
Switch off power and disconnect the power cord. The 24 VDC LVPS requires a
5 VDC enable signal to operate. Ensure proper operation of the 5 VDC LVPS
before proceeding.
1.
Remove the rear cover and 24 VDC PS metal shield.
2. Connect AC power and switch the printer ON.
3. Check for proper AC voltage at the connector at the bottom of the LVPS. If not
present, go to "Troubleshooting AC Power" on page 4-16.
4. Check for the 5 VDC enable signal at P505-3 (grey wire).
5.
If not check the same signal at the engine interface board P537-6. If not
present, replace the engine control board, then the engine interface board.
6.
Check for 24 VDC at any of the orange wires of connector P502 at the top of
the LVPS.
7.
Unplug the connector and retest.
8. If still no voltage, replace the LVPS. If the voltage returns check all 24 VDC
circuits for shorts to frame ground in the wiring harness, engine board, relay
board and interlock circuit.
4-18 Phaser 7750 Printer Service Manual