Lexmark T640 Service Manual page 159

FRU
4 HVPS cable
(part of front
harness cable)
System board
Print quality—blank page
FRU
1 Print cartridge
2 High voltage contact
3 HVPS
4 Front cable harness HVPS
section
5 Printhead assembly
Print quality—random marks
Service tip: The primary cause of random marks is due to loose material moving around inside the printer and
attaching to the photoconductor, charge roll, or transfer roll.
Symptom
1 Random marks
Action
Check the continuity of the HVPS cable. If incorrect, replace the
cable assembly. If correct, replace the system board.
Action
Check the print cartridge for damage, especially the PC drum contact
on the cartridge.
Check the PC drum contact on the right side frame for damage, PC
drum contact wear or contamination. If the contact is bent or
damaged, replace the contact.
Note: Inspect the HVPS PC drum contact on the board for damage
or contamination.
Check the fuse on the HVPS. If open, replace the HVPS. Check the
voltages at J22 on the system board. Measure the following voltages
from connector J22 to printer ground:
• Printer Idle
J15-5 measures +24 V dc
• Printer Printing
J15-5 measures +24 V dc
If the voltages at J10-5 are incorrect, replace the system board.
Check the front cable harness at J15 on the system board and at
CN1 on the HVPS to make sure the harness is connected properly. If
connected properly, check the continuity of the cable harness. If there
is no continuity, replace the front cable harness.
Generally a 93x service error is posted if the printhead assembly fails
and the printer does not give a blank copy symptom.
The printhead used in the printer does not have a mechanical shutter
as previous laser printers. The printer is interlocked through the front
top cover interlock switch.
Action
Check the print cartridge for loose or foreign material that might be
on the photoconductor. Check the transfer roll and charge roll for any
pieces of material that are stuck to the rolls.
4061-xx0
2-117
Diagnostic information