Epson Stylus pro 7700m, Service Manual

Page: 43 / 139

The figure below shows a block diagram of the power supply circuit (C137 PSB/PSE). The power switch is
equipped with a secondary circuit that allows the CPU to remain active for a while after the printer is turned
off. This allows the printhead to return to the capping position after power has been turned off. The CPU,
which is mounted on the C164 MAIN Board, always monitors the PSC (Power On/Off) signal. If this signal
goes LOW, the CPU resets each device after performing the head-capping sequence.
Also, this board
employs the RCC (Ringing Choke Converter) switching system. The AC voltage is first input to the filter
circuit for higher harmonics absorption, and then input to the rectification and smoothing circuit, converting it
into DC voltage. This DC voltage is then input to the switching circuit for the switching operation. Along
with the switching operation on the primary side, +35 VDC is generated after passing through the +35 V line
voltage detection circuit. This +35 VDC output level is stabilized. This +35 VDC is also input to the +5 VDC
generation circuit to generate a 5 VDC.
1. +5 VDC line over voltage protection circuit
The output voltage level of +5 V line is monitored by Zener diode ZD53. If the voltage level e7 V,
the status is fed back to the primary switching circuit through a photocoupler (PC1) to stop the +35 V
generation.
2. +5 VDC line over current / over voltage control circuit
The output current is monitored by detection resistor R53 and fed back to +5 VDC generation switching
control IC51, which monitors the output voltage. This information is input to the internal comparator, which
outputs a HIGH signal to turn off transistor Q51 when the voltage or current becomes abnormal.
3. +35 VDC line over voltage protection circuit
The output level is monitored by Zener diode ZD36. If the voltage level e36 V, photocoupler PC1 is
activated. This stops primary switching circuit operation.
4. +35 VDC line drop protection circuit
The output level of +35 VDC line is monitored by a detection circuit that consists of Zener diodes ZD51 and
ZD81 to 84. This circuit feeds back the output voltage level status through a photo- coupler to the primary
switching circuit to control the ON/OFF time of the switching transistor for constant output voltage.
Ph o to
Co u p l e r
S mo o t h i n g
Circuit S mo o t h in g
Circu it
Filte r Circui t
F u s e
F 1
L1,R1 C 1- C4
D B 1 C 1 1
M a in S wi tc hi n g
Circuit
Q 1
Tr
a
n
sf
or
m
e
r
T 1
C 5 1
+ 3 5 V D C
Drop Prote ctio n
Circuit
ZD51, 81-84
TL 49 4
+5 V DC
Ove r Vo lta ge
Protection Circuit
Z D 5 2
Z D 5 3
P C 1
Z D8 6 ,
C 8 2
P -O FF Si g n a l
C1 6 4 MAIN
Power SW
on Pane l
Ove r V o lt a ge
Prot ec tio n
Ci rc ui t
Fe e d b a ck
Circuit
Ful l -wa ve
Rectifier Circuit
P-OFF Dete c tion
and Dela y Circuit
Figure 2-16. Cap Mechanism
Stylus Pro Service Manual Operating Principles
Rev.A 2-13