Phaser 7700 Color Laser Printer Service Manual 3-89Troubleshooting Power Supplies and InterlocksTroubleshooting AC Power1. Verify that the AC Input Voltage is present and within specifications.2. Verify that the Reset button on the GFI is depressed.3. Reconnect AC power. If the GFI trips immediately with the Power switchOff, disconnect AC power, remove the rear cover and metal shields. Checkfor shorts in the AC Circuit from the GFI to the Noise Filter, the AC DriverBoard and up to the Power Switch.4. Switch the printer on. If the GFI trips, unplug the printer, remove the fuser,then retest. Disconnect AC power, remove the rear cover and metalshields. Check for shorts in the AC Circuit from the Power Switch back tothe AC Driver Board and to the bottom connector on the three Low-voltagePower Supplies.5. Remove the rear cover and the two metal shields. Connect AC Input andswitch the printer On. Check for AC voltage at:■ J72 on top of the GFI, if not present replace the GFI.■ Between FS76 and FS77 of the Noise Filter, if not present replace theNoise Filter.■ Into and out of the Power Switch, if not present replace the PowerSwitch.■ The connector at the bottom of the +3.3 VDC, +5 VDC and +24 VDCLVPS, if not present replace the AC Drive Board.Note The GFI, Noise Filter and AC Drive Board are all part ofthe AC Electrical Chassis, see (RRP 49, on page 7-214).Troubleshooting the Low-voltage Power Supplies+3.3 VDC, +5 VDC and +24 VDC voltages are supplied by individual LVPSboards. The 24 VDC LVPS requires the presence of a +5 VDC enabling signalto operate.Note Before troubleshooting power supply problems,disconnect the Lower Tray Deck or Finisher, if installed,and restart the printer. Verify the problem is still presentor refer to the appropriate option troubleshooting section.1. Verify the printer is plugged in and the GFI is not tripped, TroubleshootingAC Power on page 3-892. Remove the Image Processor Board cover and metal plate. Disconnect theRelay Board Power Connector J300.3. Turn the printer On. Check for +3.3 VDC at J300-1, -2, -3 & -11. Check for+5 VDC at J300-7. If 5 VDC is present check for +24 VDC at J300-9.4. If no DC voltages are present, Troubleshooting AC Power on page 3-89.5. If +5 VDC is present but +3.3 VDC is not, Troubleshooting the +3.3 VDCand +5 VDC LVPS on page 3-90.6. If +3.3 VDC is present but +5 VDC and +24 VDC are not, Troubleshootingthe +3.3 VDC and +5 VDC LVPS on page 3-90.7. If 5 VDC is present but 24 VDC is not, Troubleshooting the +24 VDC LVPSon page 3-90.
