Canon LBP-1210 Service Manual page 101

AC power is supplied to the low-voltage power supply circuit on the engine controller by turn-
ing ON the power switch (SW101).
The AC power is converted into +24VDC, +5VDC, and +3.3VDC in this circuit, required in the
printer. The +24VDC is supplied to the drives in the load system such as the main motor, scan-
ner motor, and solenoids, and also to the high-voltage power supply circuit. The +5V is supplied
to laser and the interface controller. The +3.3VDC is supplied to the sensors and the ICs on the
engine controller.
The +24VDC is divided into +24V, which is constantly supplied from the low-voltage power
supply circuit, and +24U, which is interrupted when the door switch (SW301) is turned OFF by
opening the top cover. This +24U is supplied to the high-voltage power supply circuit and fix-
ing heater safety circuit on the engine controller. Also, it functions as the DOOR OPEN DETEC-
TION (DOSNS) signal. The CPU detects door open with this signal.
b. Protective functions
This circuit utilizes overcurrent and overvoltage protective functions. These functions automat-
ically interrupt output voltage to prevent power supply failures due to an excessive current flow
or abnormal voltage generation, caused by short-circuit on the load side.
If the overcurrent or overvoltage protective function is activated and no DC voltage is output
from this circuit, turn OFF the printer, rectify the problem in the faulty load, and then turn the
power ON again.
The circuit contains a fuse (FU101), which breaks and cuts off power supply if overcurrent
flows through the AC line.
CHAPTER 2
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