Kyocera Mita DC-1560, Service Manual

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1AF
2-3-2
capacitor C101 in the rectifying circuit. The switching circuit turns FET Q101 on and off via
switching control IC1, turning current to the primary coil of switching transformer TRNS on
and off. The 24 V DC smoothing/output circuit converts the current induced in the secondary
coil of TRNS into a stable 24 V DC output via diode D201 and smoothing capacitors C201
and C207. The 5 V DC smoothing/output circuit converts the 24 V DC output from the 24
V DC smoothing/output circuit into a stable 5 V DC using regulator IC3. Switching control
IC1 regulates the 24 V DC supply by controlling the switching operation of FET Q101
depending on the signal fed back by the output feedback circuit via photocoupler PC1. If an
overvoltage occurs on the 24 V or 5 V DC output, the output feedback circuit sends that
information to switching control IC1 via photocoupler PC2, inhibiting IC1.
• AVR circuit section
The AVR circuit section consists of the PWM signal/voltage converter circuit, a halogen
lamp control subsection with the halogen lamp light intensity control IC (HIC), and a
switching subsection with thyristors TH601 and TH602 that turn the fixing heater (H) and
halogen lamp (HL) on and off.
Control signal H REM from the main PCB turns photocoupler PC4 on when low. This allows
current to flow from transistor Q602 to photocoupler PT1, turning PT1 on, which applies a
trigger voltage to the gate of thyristor TH602, causing it to conduct and allow current to flow
to fixing heater (H) to turn it on. Transistor Q602 is turned on by the zero-crossing signal from
the halogen lamp light intensity control IC (HIC), so thyristor TH602 conducts and the
current flows to the fixing heater every time 0 V is crossed.
The halogen lamp light intensity is controlled by control signal HL CONT from the main PCB.
HL CONT is a PWM signal turned on and off at a duty ratio set by the halogen lamp light
intensity data. This signal is converted into a voltage by the PWM signal/voltage converter
circuit and is output to the halogen lamp light intensity control IC (HIC). This adjusts the
phase of the photocoupler PT2 on-timing based on the halogen lamp light intensity data
converted into a voltage, using an internal zero-crossing signal as a reference. When
photocoupler PT2 is turned on, a trigger voltage is applied to the gate of thyristor TH601,
changing the time that TH601 conducts. This changes the level of the voltage applied to the
halogen lamp terminals, so regulating the halogen lamp light intensity.