Sharp LC-20AV7U Service Manual - Page 19

Power Supply

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1. POWER SUPPLY SECTION FLOW CHART NO.1 The power cannot be turned on. No Is the fuse (F601) normal? Yes Is normal state restored when once unplugged No power cord is plugged again several seconds? Yes Is the AL +12V line voltage normal? No Yes Check each rectifying circuit of the secondary circuit and service it if defective. FLOW CHART NO.2 The fuse blows out. See FLOW CHART No.2 Check if there is any leak or short-circuiting on the primary circuit component, and service it if defective. (Q601,Q603,T601,D605,D606,D607,D608,C615) Check the presence that the primary component is leaking or shorted and service it if defective. Check the presence that the rectifying diode or circuit is shorted in each rectifying circuit of secondary side, and service it if defective. After servicing, replace the fuse. FLOW CHART NO.3 When the output voltage fluctuates. Does the photocoupler circuit on the No secondary side operate normally? Yes Check IC601,D613,D614 and their periphery, and service it if defective. FLOW CHART NO.4 When buzz sound can be heard in the vicinity of power circuit. Check IC601,Q913,D909,D933 and their periphery, and service it if defective. Check if there is any short-circuit on the rectifying diode and the circuit in each rectifying circuit of the secondary side, and service it if defective. (IC901,IC904,IC905,D901,D902,D903,D906,D909,D911,D931 ) FLOW CHART NO.5 +35V is not output. Is approximately 35V voltage supplied to the cathode of D909? Yes Check if there is any leak or short-circuit on the loaded circuit, and service it if defective. No Check D909, C907 and their periphery circuit, and service it defective. 7-2 A7144_45TS

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7-2
A7144_45TS
1.
POWER SUPPLY SECTION
Check IC601,D613,D614 and their periphery,
and service it if defective.
The power cannot be turned on.
The fuse blows out.
FLOW CHART NO.1
FLOW CHART NO.2
Is normal state restored when once unplugged
power cord is plugged again several seconds?
Check if there is any leak or short-circuiting on the
primary circuit component, and service it if defective.
(Q601,Q603,T601,D605,D606,D607,D608,C615)
Yes
No
Yes
Is the fuse (F601) normal?
See FLOW CHART No.2 <The fuse blows out.>
No
Yes
Is the AL +12V line voltage normal?
No
Check each rectifying circuit of the secondary
circuit and service it if defective.
Check the presence that the primary component
is leaking or shorted and service it if defective.
Check the presence that the rectifying diode or circuit
is shorted in each rectifying circuit of secondary side,
and service it if defective.
After servicing, replace the fuse.
When the output voltage fluctuates.
FLOW CHART NO.3
Does the photocoupler circuit on the
secondary side operate normally?
No
Yes
Check IC601,Q913,D909,D933 and their periphery,
and service it if defective.
When buzz sound can be heard in the vicinity of power circuit.
FLOW CHART NO.4
Check if there is any short-circuit on the rectifying diode and the circuit in each rectifying circuit of the secondary side,
and service it if defective. (IC901,IC904,IC905,D901,D902,D903,D906,D909,D911,D931 )
Check if there is any leak or short-circuit on
the loaded circuit, and service it if defective.
+35V is not output.
FLOW CHART NO.5
Is approximately 35V voltage supplied to the
cathode of D909?
No
Yes
Check D909, C907 and their periphery circuit, and
service it defective.