Directview LCD Training 26 Circuit Descriptions
CIRCUIT DESCRIPTIONS
No power
from +18V
Output terminal
shorted
D
E
U903 Error, no
input of L812
No power
from +5VS
Output terminal
shorted
#7 pin bias power
of U902 is abnormal
(normal: 15V-25V)
Check/replace
R937-R939, U903
(FAN7554), Q802,
D802, CR801
T802 Error
Replace T802
Check +5V
Speripheral parts
for patternl short
Problem lies
elsewhere
No
No
Yes
No No No
Yes
Yes
Yes
Yes
Check +18V
peripheral parts for
patternl short
Problem lies
elsewhere
Check/replace
U802
(PQ1CG203) &
D916 (SB560)
POWER SUPPLY DESCRIPTION
If the AC Input voltage (1) is confirmed, this voltage is adjusted as a DC wave form through the EMI
filter (2) and the first rectifier/filter (3). This adjusted wave form is input to PFC circuit (4), Power
Factor Correction). The output voltage (+390Vdc) of the PFC circuit becomes a main input voltage of
the MAIN (5) and standby switching part (10). Using elements such as the FET and PWM IC, the
switching parts (5, 10) convert this high DC voltage (390Vdc) to a spherical wave with a high frequency.
To keep the secondary adjusted voltage regular and safe with changing input voltage and output load,
the output voltage is monitored and fed back to the switching part through a control circuit (9).
BLOCK 2 works as a forward converter by receiving input from BLOCK 1 and supplying MAIN DC (+24V
and +12V) voltage and the step down circuit (8) supplies +18V. BLOCK 3 works as a flyback converter
by receiving the input of BLOCK 1 and supplying +5V for standby. A protection circuit is built into the
switching part (5, 10) to protect over current, short, or over voltage of the secondary output. When
overheating occurs, this circuit protects the output and switches the thermal switch (15) to radiator.
The PFC circuit protects against fire or other accidents by turning the AC voltage off. If the OFF signal
is transmitted to the PFC circuit (4). Only the +5V circuit for standby works and others are turned off to
minimize power consumption.
Thermal
Switch
PT800
Rectifiers
and Fiter
BD801,
C806, etc.
EMI Filter
L801, L802
C801~5,
etc.
P800
Switching
Elements,
OVP, OCP
Circuit
Standby
Q802, U903,
etc
Feedback
Circuit &
Isolation
PH801,
CR802, etc
Output
Rectifiers
and Filters
D802,
C825, etc
Isolation
Power
Transformer
T802
PFC Circuit
T801, Q801,
U901, D801,
C811, C812,
etc.
Switching
Elements,
OVP, OCP
Main Circuit
Q804, U902,
D912, etc
Isolation
Power
Transformer
T803
Output
Rectifiers
and Filters
D803~D805
L805, C827,
C823, etc
390Vdc
Control
Isolation
PH802,
PH803, etc
Feedback
Circuit &
Isolation
PH804,
CR801, etc
Step Down
Circuit
U802, D916,
L807, etc
BLOCK 1
BLOCK 2
BLOCK 3
12V
24V
18V
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