Epson PhotoPC 2100Z, Service Manual

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PhotoPC 2100Z Revision A
Operating Principles Overview 42
2.1.3.2 Operating Principles of Power Supply Circuit
The control IC (IC1) in the power supply circuit has a 2-channel control system. One
channel is used for voltage down by L81 to generate 3.3 V. The other channel is used
for voltage boosting and voltage down by the transformer T21 to generate four outputs,
namely, +3.3 V, +5 V, +18 V and -8 V.
PC3.3V and PL3.3V are supplied from the 3.3 V of L81 by turning on and off the
switching circuit of Q91 and Q94.
Transformer T21 is a flyback circuit of +3.3 V.
+1.8V is generated from +3.3 V and stabilized by the regulator Q71.
+D3.3V is turned on and off by the switching circuit consisting of Q61 of +3.3 V.
+5V is stabilized by Q31.
+C18V is stabilized and turned on and off by Q41.
+C16V is generated from +C18V and stabilized by Q161.
CM7V is generated from -8V and stabilized by Q51.
BK_8V is generated by self-excitation transformer T1 and Q4.
2.1.3.3 Power Supply Circuit on the Main Circuit Board
A power supply circuit (U1806) of 4.8 V is provided for motor drive.
To supply -32V for LCD brightness adjustment, the charge pump circuit U1603 is
provided.
2.1.3.4 Power Supply Circuit on Flash Circuit Board
The backlight is turned on by inverter (alternating current waveform) output of BK_6V
by t3103. The output connector is CN3104.
2.1.4 Operating Principles of Flash Circuit
The major functions of the flash circuit are to charge the flash capacitor at the flash
firing voltage and to fire the xenon flash lamp.
The flash firing voltage is boosted to about 300 V by the oscillating transformer T3101
and charges the flash capacitor. The control signal ST_ON from the 8-bit CPU turns on
the transistor Q3105 to start flash charge. Flash charge is completed when Zener diode
D3106 sends the ST_OK signal to the 8-bit CPU.
The charge in the flash capacitor is applied to the trigger transformer T3102 by IGBT
Q3107 to fire the flash lamp. Flash firing is controlled by the DD_TRIG signal (5V
level).
2.1.5 Fuses
The power supply circuit has three fuses.
On the Main Circuit Board, a fuse is mounted for power to the motor.
The fuse for flash circuit is mounted on the Flash Circuit Board.