LG SNC4R Service Manual page 42

PROTECTION ERROR
No display or No Sound.
3-2. B(BURNT) PROTECTION
3-2-1. Solution
Replace MAIN board.
3-2-2. How to troubleshoot (Countermeasure)
1) Check voltage 12 V of IC703 at pin1 ~ 2, if 12V has problem refer to STEP 1-1.
2) If 12 V is OK, replace MAIN board.
3-2-3. Service hint (Any picture / Remark)
F L +
F L -
F R +
ONE POINT REPAIR GUIDE
R702
AMP_PROTECT
2
ZD702
NC R703
Z02W3.9V
3 1
C706
PGND
AMP_PDN
FR_OUT_N
FR_OUT_P
VCC33 1
R716 R715
4.7K 47K
FL_OUT_N
FL_OUT_P
AMP_FAULT
R784
DC_PROTECTION
C707 C708
100pF 100pF
R 7 8 5
IC703 IC703
< MAIN board bottom view >
+12V
27K
ZD701 NC
KDZ13V-RTK/P
10K
IC703
C730 1uF
100pF
1
C731 100nF
BST_A
GVDD_AB
2
C741 10uF
BST_B
VDD
3
R775 47K
OC_ADJ
R777 100 4
/RESET
5
OUT_A
INPUT_A
6
OUT_A
INPUT_B
7
C736 100pF
2
PVDD_AB
C_START
ZD703
8
C737 1uF
Z02W3.9V
PVDD_AB
DVDD
9
3
PVDD_AB
GND
R7A2
NC 10
OUT_B
GND
11
PGND
GND
12
GND
13
C738 1uF
OUT_C
AVDD
14
PVDD_CD
INPUT_C
15
PVDD_CD
INPUT_D
16
R782 100
PVDD_CD
/FAULT
17
R783 NC
OUT_D
/OTW
18
2.2K
OUT_D
/CLIP
19
M1
20
M2
R7A3
21
0
M3 BST_C
22
C739 1uF
GVDD_CD BST_D
PGND
Q 7 0 8
R 7 B 4
Q 7 0 9
R 7 B 0
C 7 3 9
R 7 8 4
R 7 8 3
R 7 8 2
C 7 3 8
R 7 7 7
R 7 7 5
C 7 3 1
Z D
3-13
Copyright © 2021 LG Electronics Inc. All rights reserved.
44
43
42
GND
41
GND
40
39
38
37
36
35
34
GND
33
GND
32
31
30
29
28
27
26
GND
25
GND
24
23
R E M O _ T P
C 3 0 6
R 3 0 6
C 3 5 1
R 3 0 1
Only for training and service purposes.
J K 5 0 2