LG SL7Y Service Manual page 31

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. IC301 System 3.3 V (No 3.3 VA)
1-2-1. Solution
Replace MAIN board.
1-2-2. How to troubleshoot (Countermeasure)
1) Please check 3.3 VA of IC301 pin3.
2) If 3.3 VA is abnormal, replace MAIN board.
3) If 5.1 VA is OK, replace MAIN board.
1-2-3. Service hint (Any picture / Remark)
5.1VA
FB305
UBW2012-121F
R 3 5 7
C 3 2 8
R 3 5 6 R 3 0 9
IC301 IC301
C 1 9 5
I C 3 0 1
L 3 0 1
L301 L301
C 3 5 5
S L 7 M A I N
E A X 6 8 3 1 4 6 0 2 V e r 1 . 0
- F R 4 - 4 L 1 . 6 T
P C B S I Z E : 2 5 9 . 5 X 6 8
2 0 1 8 . 1 1 . 2 2
ONE POINT REPAIR GUIDE
[5.1VA TO 3.3VA]
IC301
VIN
4
C309
C367
10uF
100nF
/10V
FB
/16V
5
R356
DGND
VOUT = 0.6*(1+R1/(R2//R3))
VOUT = 0.6*(1+100K/((24K*240K)/(24K+240K)))
= 0.6*(1+100K/21.82K) = 3.350V
C 3 0 2
C 3 5 6
I C 3 0 4 R 3 9 3
R 3 9 2
R 3 2 9
< MAIN board top view >
L301
SW
470nH
3
GND
2
C328
EN/PG
R357
1
C322
47pF
100K
10uF
/10V
(1%)
4.7K
R1
R309
R316
R2
240K R3
24K
(1%)
(1%)
DGND DGND
C 3 8 6
F B 3 1 8
C 3 8 5
R 3 7 2
C 3 8 3
R 3 7 1
C 3 8 4
R 3 7 5
3-6
Copyright © 2019 LG Electronics Inc. All rights reserved.
3.3VA
NC
R385
0OHM
C354 C364 C370
10uF 10uF 100nF
/10V /10V /16V
DGND
R C F 0 1
Z D 1 0 1
T P 1 6 6
R 1 2 8
R 1 2 9
R 1 N 7
R 1 N 3
T P 1 6 9
T P 1 7 0
R 1 3 0
R 1 3 1 R 1 3 2
Only for training and service purposes.