Brother International HL-720 Service Manual - Page 69

Black and blurred horizontal stripes, Dropout, PCB. If

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I-7 Black and blurred horizontal stripes Possible cause Scratch on the drum Toner stuck on the develop roller Step 1 2 Check Are the horizontal stripes at 94mm intervals? Are the horizontal stripes at 17mm intervals? Scratch on the fixing roller 3 Are the horizontal streaks at 50 mm intervals? Result Yes Yes Yes Remedy Replace the drum unit. Print several sheets and see what happens. The problem will disappear after a while. Replace the fixing unit. I-8 Dropout Possible cause Transfer failure High-voltage power supply failure Step 1 2 Check Is the transfer roller soiled? Is it scratched? Open the top cover and measure the voltage at the transfer electrode plate at the right side while printing with the interlocks defeated. Is the voltage correct? Result Yes Yes Remedy Replace the drum unit. Check the harness connection between the high-voltage power supply and the panel sensor PCB. If the connection is normal, replace the highvoltage power supply PCB.

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I-7
Black and blurred horizontal stripes
Possible cause
Step
Check
Result
Remedy
Scratch on the
drum
1
Are the horizontal stripes at 94mm
intervals?
Yes
Replace the drum
unit.
Toner stuck on
the develop
roller
2
Are the horizontal stripes at 17mm
intervals?
Yes
Print several sheets
and see what
happens.
The problem will
disappear after a
while.
Scratch on the
fixing roller
3
Are the horizontal streaks at 50 mm
intervals?
Yes
Replace the fixing
unit.
I-8
Dropout
Possible cause
Step
Check
Result
Remedy
Transfer failure
1
Is the transfer roller soiled? Is it
scratched?
Yes
Replace the drum
unit.
High-voltage
power supply
failure
2
Open the top cover and measure
the voltage at the transfer electrode
plate at the right side while printing
with the interlocks defeated.
Is the voltage correct?
Yes
Check the harness
connection between
the high-voltage
power supply and
the panel sensor
PCB. If the
connection is normal,
replace the high-
voltage power supply
PCB.