LG LSC27990TT Service Manual page 71

2-9. MICOM
Problems Symptom
Bad PCB All display
electric power. LCD are off.
Abnormal
display LCD
operation
Causes
Bad connection Bad connector
between Main PCB connection from main
and display circuit. PCB to display PCB.
Defective PCB PCB transformer
transformer. winding is cut.
PCB transformer
temperature fuse is
burnt out.
Defective PCB electric Defective regulator IC
circuit parts. (7812, 7805).
PCB electric terminal
fuse is burned out.
STR Parts are
damaged.
Bad connection Lead Wire connecting
between Main PCB main PCB and display
and display circuit. PCB is cut or connector display PCB with a tester.
terminal connection is
bad.
Defective LCD. Defective LCD.
Checks
Visual check on connector Reconnect
connection. connector.
Check resistance of PCB Replace PCB
transformer input and output transformer or PCB.
terminals with a tester.
(If resistance is infinity, trans
winding is cut).
Check voltage at input/output Replace regulator.
terminals.
Check fuse in PCB electric Replace PCB fuse.
terminal with a tester.
Check if STR No. 2 and 3 pins Replace parts.
are cut when power is off.
Check Lead Wire terminals Reconnect Lead
connecting Main PCB and Wire and directly
connect defective
contact terminal to
Lead Wire.
Check if all LCD are on when Replace display
Main PCB Test switch is PCB.
pressed (or when both freezer
key and power freezer key are
pressed at the same time for
more than one second.)
Measures Remarks
Applicable to
model without
dispenser.
Refer to electric
circuit in circuit
explanation.
Applicable to
model with
dispenser.
Refer to display
circuit in circuit
explanation.