Brother GTX-4 Service Manual page 342

If printer is not powered ON
(1) Confirm whether the power cable is connected correctly.
(2) Confirm whether the front cover is properly closed.
(3) Confirm ON / OFF condition of power indicator lamps.
If lamps LD5, LD4, LD8 and LD7 are all OFF, -> Power cable, power source circuit board, power source circuit
board plate assembly, AC inlet, fuse and power source transformer
If LD5 is ON and lamps LD4, LD8 and LD7 are OFF, -> power source circuit board
If LD5 and LD4 are ON and LD8 does not respond to the ON/OFF of power switch -> power source circuit
board, power switch
If lamps LD5, LD4 and LD8 are ON while LD7 is OFF, -> Power unit, power source circuit board, cover open
switch, DC power source harness
If lamps LD4, LD5, LD7 and LD8 are ON while either of the lamps LD1, LD2, LD3, LD6 or LD7 is OFF, ->
Power source circuit board
Lamps LD4, LD5, LD6, LD8, LD1, LD2, LD3, LD6 and LD7 are all ON -> Main power source harness, color
power source harness, white power source harness
Disassembly / Replacement / Adjustment
6-151