I-2
Dark
Possible cause
Step
Check
Result
Remedy
Contrast failure
1
Is the contrast adjustment dial at
the center click position?
No
Set it to the center
click position or
reasonable position.
Corona failure
(soiled wire)
2
Is the corona wire soiled?
Yes
Clean the corona
wire.
Corona failure
(contact failure)
3
Are the corona electrodes between
the printer body and drum unit
soiled?
No
Clean both
electrodes.
Drum unit
failure
4
Is the problem solved when the
drum unit is replaced?
No
Replace the drum
unit with a new one.
I-3
Completely blank
Possible cause
Step
Check
Result
Remedy
Developing bias
contract failure
1
Are the developing bias contacts
between the printer body and drum
unit solid?
Yes
Clean the electrodes
at both sides.
Scanner
harness
connection
failure
2
Is the scanner LD control harness
connected normally?
Is there any play in the connection?
Yes
Connect the
connector correctly.
Main / panel
sensor PCB
connection
failure
3
Are printing signals being input to
the scanner?
No
Replace the main
PCB or Panel sensor
PCB.
Scanner unit
failure
4
Problem of scanner interlock lever.
Scanner mirror is bending or
coming off.
Yes
Replace the scanner
unit.
Drum unit
failure
5
Defective D/R nip of drum unit.
Yes
Replace the drum
unit.
Summary of Contents for HL-720
Page 1: ...SERVICE MANUAL MODEL HL 720 730 730Plus R LASER PRINTER ...
Page 36: ...II 19 1 3 10 Engine I O HL 720 Fig 2 21 shows the engine interface circuit Fig 2 21 ...
Page 37: ...II 20 HL 730 730Plus Fig 2 22 shows the engine interface circuit Fig 2 22 ...
Page 61: ... Fig 3 18 2 4 1 1 1 ...
Page 92: ...SERVICE MANUAL MODEL HL 760 R LASER PRINTER ...
Page 109: ...II 8 1 3 4 DRAM Two 4M bit DRAMs x 16bits are used as the RAM Fig 2 6 ...
Page 113: ...II 12 1 3 10 Engine I O Fig 2 12 shows the engine interface circuit Fig 2 12 ...
Page 114: ...II 13 1 3 11 Paper Feed Motor Drive Circuit Fig 2 13 ...
Page 133: ...Appendix 2 Main PCB Circuit Diagram 1 3 CODE UK3227000 B48K272CIR 1 3 NAME ...
Page 134: ...Appendix 3 Main PCB Circuit Diagram 2 3 CODE UK3227000 B48K272CIR 2 3 NAME ...
Page 135: ...CODE UK3227000 B48K272CIR 3 3 NAME Appendix 4 Main PCB Circuit Diagram 3 3 ...