3-5
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
ONE POINT REPAIR GUIDE
1.
NO BOOTING WHEN YOU TURN THE UNIT ON, NO MESSAGE OR “HELLO”
ON FRONT PANEL
When you turn on your set, no message on the front panel, and stand-by LED doesn’t work.
1-1. IC302 System 12 VA (No 12 VA)
1-1-1. Solution
Replace MAIN board.
1-1-2. How to troubleshoot (Countermeasure)
1) Please check 25 VA of IC302 pin2 (VIN).
2) If 25 VA is abnormal, please check adapter.
3) If 25 VA is OK, but 12 VA is abnormal pin3 of IC302 (VOUT), replace MAIN board.
1-1-3. Service hint (Any picture / Remark)
< MAIN board top view >
2
R405
R407
R408
R409
R3A3
R3A4
R3A5
R3A6
CN402
R5A5
X401
C5A1
C5A2
F300
F301
C431
C432
C433
C434
C435
C436
C437
C438 C439
C440
C446
Q300
Q301
ZD504
L300
L301
L302
FM
RR503
RR505
RR506
RR507
RR508
RR509
RR510
RR511
RR512
RR513
RR514
RR515
RR516
RR517
FB303
FB304
FB305
F
R303
RCF500
FB314
FB316
JK502
FB318
R308
R310
R312
R315
RC502
3
4
5
6
RC509
R327
0
CN500
11
2
CN502
3
4
5
8
9
R528
R338
R339
2
3
C300
R4C3
C307
C308
C309
C310
40
C311
541
C312
C313
C314
C315
C316
C317
C318
C319
R549
C4A4
C320
C4A5
C321
C4A6
C322
R552
C323
R365
R559
R366
R368
C330
C331
561
C333
R370
C334
R371
R375
R380R381
TP_GND
C547
C354
C548
C549
C355
C356
WR505
WR506
WR507
WR508
WR509
D301
WR510
C364
WR511
WR512
WR513
C367
C370
C379
L406
L407
IC300
C381
IC301
C382
IC302
C383
IC309
C390
IC310
IC311
C391
WC502
C392
C393
IC313
WC503
C394
WC504
C395
WC505
WC506
WC509
WC514
WC515
WC519
WC520
WC522
WC523
R4N4
FB401
R4N5
FB402
FB403
FB404
R4N8
R5F2
R5F1
C5F2
C5F1
FB510
IC402
C306
100nF
DGND
C312
10uF
/35V
R328
100K
R335
100K
R300
51K
(1%)
DGND
PVDD
C307
100nF
/50V
C351
33pF
PWR_GD
C300
10uF
/35V
12VA
R305
3.3K
(1%)
C323
10uF
/35V
NC
DGND
R301
47K
(1%)
FB303
UBW2012-121F
R306
22
C320
10uF
/35V
C302
100nF
C313
10uF
/35V
IC302
1
PG
2
IN
3
SW
4
GND
5
BST
6
EN/SYNC
7
VCC
8
FB
L302
10UH
DGND
R307
390K
R340
56K
[25VA TO 12VA]
VOUT = 0.792x(47K/3.3K+1)= 12.072V
IC302
L302
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