One Point Repair Guide; Booting When You Turn The Unit On, No Message Or "Hello" On Front Panel - LG SNC4R Service Manual

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)
PWR_GD
R305
3.3K (1%)
VOUT = 0.792x(47K/3.3K+1)= 12.072V
L 3 0 1
I C 3 0 1
R 3 0 8
R 5 5 2
R 5 5 9
5 6 1
C 3 9 2
5 4 0
C 3 9 1
R 5 4 1
C 3 8 1
C 3 8 2
C 3 8 3
F B 3 1 4
R R 5 0 3

ONE POINT REPAIR GUIDE

[25VA TO 12VA]
IC302
8
FB
7
VCC
6
EN/SYNC
5
BST
R306 22
DGND
F B 5 1 0
C 5 F 1
C 5 F 2
R 5 F 1 C 3 9 5
C 3 3 0
R 5 F 2
R 3 7 1 C 3 9 3
CN502
C 3 9 4
I C 3 1 3
C 4 3 8 C 4 3 9
C 3 3 1
R 4 0 9
C 3 3 3
F B 3 1 6
R 4 0 8
C 3 3 4
C 4 4 0 I C 4 0 2
C 4 3 2
L 4 0 7
< MAIN board top view >
1
PG
2
IN
L302
3
SW
10UH
4
GND
DGND
C306
100nF
L 3 0 0
F B 3 0 4
R 3 2 7 R 3 1 2
R 3 0 3
R 3 1 0
C 5 4 7
F M
T P _ G N D
F B 4 0 4
F B 4 0 3
C N 4 0 2
3-5
Copyright © 2021 LG Electronics Inc. All rights reserved.
PVDD
FB303
UBW2012-121F
C307
100nF
/50V
12VA
DGND
C323
C300
C320
10uF
10uF
10uF
/35V
/35V /35V
NC
DGND
R C F 5 0 0
C 5 4 9
Z D 5 0 4
Q 3 0 0
C 5 A 1
C 5 A 2
I C 3 0 9
L302 L302
L 3 0 2
R 5 2 8
C 3 1 3
C 5 4 8
C 3 1 2
C 3 2 3
C 3 0 7
IC302 IC302
C 3 0 0
C 3 2 0
2
Only for training and service purposes.
Q 3 0 1
F B
C 3 7 9
F 3 0 1
F 3 0 0