Brother HL-2600CN Service Manual page 327

Error Code L1 (Beam Detecting Error)
Concerned Part Scanner Unit
Confirm the connection of an scanner unit connector.
NO
Is the connector PDCN properly connected ? Connect the connector properly.
Are the connector LCN1 and LCN of MCTL properly connected ?
YES
Is L1 error cleared ?
NO
YES
Replace the scanner unit.
YES
Is L1 error cleared ?
NO
Replace the MCTL PWB 2. Job is complete.
MCTL
PD LDU
SGND
PDCN
Scanner Unit
LCN +5V-1R
BDT
Laser Diode
LCN1 SM
SM
LCN3
20