Brother Facsimile Equipment MFC7420 - Manual (Page 194)

Confidential 9 - 6
The solution when Error Code 76,77,78 shown in the machine:
It’s possible that the temperature of the heater rises when these kinds of error occur. Therefore, the
heater is programmed to turn off the power for 10 minutes after the switch is on for the safety
concern when the error occurs.
To help the heater work properly, it’s necessary to follow the operating procedures as below after
taking measures against the cause of the error.
1. Turn off the switch. Wait until the temperature of the heater lowers enough.
2. Turn on the switch.
3. Display the maintenance mode, then switch to the desired mode or keep the power on for 10
minutes.
Error Code
(Hex)
Symptom Probable Cause Solution
Thermistor in the fixing
unit defective Replace the thermistor in
the fixing unit.
PS PCB unit defective Replace PS PCB unit.
76
Heater overheats.
Main PCB defective Replace the main PCB.
77 The power supply is turned
off when the error 76 or 78
occurs.
--- ---
Poor connection in the
harness of the halogen
lamp Reinsert and adjust the
harness
Halogen lamp defective Replace halogen lamp.
Thermistor defective Replace the thermistor
PS PCB unit defective Replace PS PCB unit.
78 Temperature of the heater does
not rise.
Main PCB defective Replace the main PCB.
79 In casing temperature sensor
harness disconnected or
broken. (Not used.)
Main PCB defective Replace the main PCB.
7A Main motor does not
synchronize with the reference
clock.
Main motor defective Replace the main motor.
7B ASIC error on the main PCB.
(Not used.)
7C-7F Not used.