Brother HL-720 - B/W Laser Printer Service Manual page 71

I-11 Poor fixing
Possible cause Step
Printing paper 1
Toner sensing 2
failure
Fixing unit nip 3
failure
Thermistor 4
failure
Check
Is thick paper more than 36 lb.
being used?
Is the problem solved by replacing
the drum unit or the toner cartridge?
(When printing is faint.)
Is the nip width in the fixing unit
insufficient?
Is the nip spring (P/R spring)
unconnected?
Measure the temperature of heat
roller surface during printing.
Is the temperature correct (160°C)?


Result Remedy
Yes Instruct the user to
use paper of the
recommended
thickness.
Yes Toner is empty.
As toner sensing is
defective, clean the
toner sensor.
If the wiper of the
toner cartridge id
broken, replace the
toner cartridge with a
new one.
Yes Connect the spring
or replace the fixing
unit.
No Replace the fixing
unit.