Brother DCP-L8400CDN Service Manual page 70

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Error code 0300
Print Unable 03
Turn the power off and then back on again.
The Lock signal of the polygon motor of the laser unit cannot be detected.
Error code 0401
Print Unable 04
Turn the power off and then back on again.
BD sensor 1 damaged.
Error code 0402
Print Unable 04
Turn the power off and then back on again.
BD sensor 4 damaged.
Step
1 Connection failure of the polygon
motor harness
2 Laser unit failure
3 Main PCB failure
Cause
Reconnect the polygon motor harness.
Replace the laser unit.
Replace the main PCB ASSY.
2-40
Remedy
Confidential