Brother HL-3450CN Service Manual page 294

Error Code
Concerned Part Toner Sensor PCB.(LED side)
Confirm the connection of a toner sensor PCB.(LED side) connector.
Is DCN7 of IOD1 properly connected with a connector of the toner sensor ?
YES
Check the voltage(LEDON-N/P)
Is a signal voltage between DCN7-7 and 9 to be a rising edge(+24V) ?
NO
Is a signal voltage between DCN1-15 and 41 to be a trailing edge ?
YES
Is E4 error cleared ?
YES
Job is complete.
E4
NO
NO
YES
NO
NO
Connect them properly.
Is E4 error cleared ?
Replace the toner sensor PCB.
Replace the IOD1 PWB.
Replace the MCTL PWB.
DCN1
MCTL
1ICN
5
SGND
41 41
LEDON-N
15
15
8-31
HL-3450CN SERVICE MANUAL
YES
Job is complete.
Toner Empty PCB.
IOD1
DCN7
9
LEDON-P
1
7
7 7
TLSCHK
2
8
8 8
SGND
3
9
9 9