LG SL4Y Service Manual page 28

NO BOOTING WHEN YOU TURN THE UNIT ON, NO MESSAGE OR "HELLO"
ON FRONT PANEL
When you turn on your set, it will blank / no message on front panel / doesn't work.
1-2. IC300 System 5.1 V (No 5.1 VA)
1-2-1. Solution
Check MAIN board.
1-2-2. How to troubleshoot (Countermeasure)
1) Please check 5.1 VA of IC300 pin2
2) If 5.1 VA is abnormal, replace MAIN board.
1-2-3. Service hint (Any picture / Remark)
C319
10pF
DGND
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
[12VA TO 5.1VA]
R346
390K
6 FB
5 EN
BST
4
R311
150K
R355
33 C303
DGND
VOUT = 0.798x((62K+8.2K)/13K+1)= 5.1V
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 >
C314
100nF
/50V
1
VIN
L300
2
SW
10UH
3
R327
GND
8.2K
(1%)
DGND
1uF (1)
R312
62K
(1%)
R310
13K (1%)
DGND
L300 L300
L 3 0 0
F B 3 0 4
R 3 2 7 R 3 1 2
IC300 IC300
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
Copyright © 2019 LG Electronics Inc. All rights reserved.
3-6
12VA
FB304
UBW2012-121F
C308
C310
10uF 5.1VA
10uF
/35V
/35V
DGND
C316
C318 C321
10uF 10uF 10uF
/16V /16V /16V
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
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
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