KPOWERSCIENCE KP3828 Series, Maintenance Manual

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8-3 Remedies for Developing Unit Errors
Errors related to the developing unit can be largely classified into the following:
1) No toner
2) Toner density too low
These errors occur under the following conditions.
No Toner
The empty condition is indicated by a signal from the toner empty sensor. To be
more specific, the PIN2 output of U39 (LM339MA) of the KMPU board becomes 5
V.
Toner density too low
This error is determined by the toner supply rate and the toner density sensor output.
Toner supplying is performed when the toner density sensor indicates that the toner is
light at the timing of toner supply monitoring. In this process, the toner supply clutch
is engaged for 1 second to cause the supply roller to rotate to thereby supply the toner.
Toner density monitoring is continued while the developing unit motor is driven, and
when the toner density sensor output does not indicate the dark condition even after
the toner is supplied 20 times consecutively, an error is output to indicate that the
toner density is abnormally low.