LG SN4A - Booting When You Turn the Unit On, no Message or Hello on Front Panel

3-6
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
ONE POINT REPAIR GUIDE
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. IC305 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 IC305 pin2
2) If 5.1 VA is abnormal, replace MAIN board.
1-2-3. Service hint (Any picture / Remark)
< MAIN board bottom view >
C314
100nF
(1)
C310
10uF
/35V
(3)
C316
10uF
/16V
C308
10uF
/35V
(3)
NC
C319
10pF
C321
10uF
/16V
C303 1uF
(1)
C318
10uF
/16V
R355
33
R303
100K
R310
13K
(1%)
R327
8.2K
(1%)
R312
62K
(1%)
12VA
5.1VA
DGND
DGND
DGND
DGND
DGND
D301
1
C
2
A
3
C
C3A3
100nF
R371
0OHM
R346
390K
R370
150K
IC305
1
VIN
2
SW
3
GND4
BST
5
EN
6
FB
L300
10UH
DGND
R302
NC
VOUT = 0.798x((62K+8.2K)/13K+1)= 5.107V
[12VA TO 5.1VA]
IC305
IC305