LG SL4Y Service Manual page 29

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.
1-3. IC301 System 3.3 V (No 3.3 VA)
1-3-1. Solution
Replace MAIN board.
1-3-2. How to troubleshoot (Countermeasure)
1) Please check 3.3 VA of IC301 pin3.
2) If 3.3 VA is abnormal, replace MAIN board.
1-3-3. Service hint (Any picture / Remark)
5.1VA
FB305
UBW2012-121F
C309
10uF
/10V
DGND
VOUT = 0.6x(1+(R357/(R309//R316)))
VOUT = 0.6x(1+100k/((240k*24k)/(240k+24k)))= 3.35V
C 3 2 4
C 3 2 7
C 3 8 8
C 3 0 4
C 3 8 7
R 3 1 9
C 5 4 5
C 5 4 6
D 5 0 2
J K 5 0 1
C 5 4 4 C 5 7 0
ONE POINT REPAIR GUIDE
[5.1VA TO 3.3VA]
IC301
IN
4
C367
100nF
FB
/16V
5
R356
R 5 A 4
R 5 A 3
C 5 1 5
C 5 5 3
R 5 0 6 R 5 0 5
C 5 8 8
C 5 7 7
L 3 0 8
F B 3 1 5
C 5 0 8
C 5 0 9
R 3 1 4
M C L K
R 5 0 7
R 5 9 8
R 5 9 9
O P 6
I C 3 0 3
O C P
R 5 1 0
R 5 A 1
R 5 A 0
R 5 7 9
R 5 A 2
R 5 3 2
R 5 8 0 R 5 8 1
R 5 8 2
R 5 3 1
Z D 5 1 1
< MAIN board top view >
L301
LX
470nH
3
GND
2
C328
EN
R357
1
47pF
100K
(1%)
4.7K
DGND
R309
R316
24K
240K
(1%)
(1%)
R 3 9 6
I C 3 1 2
X 5 0 0
C 5 1 8 C 5 1 7
R 5 3 0
IC301 IC301
R 5 5 4
R 5 1 8
R 5 5 3
R 5 2 1
R 5 8 4
I C 5 0 1
R 5 5 2
R 5 3 5
R 5 5 9
C 5 6 4
R 5 6 1
R 5 2 0
R 5 1 9
R 5 8 6
R 5 4 0
R 5 8 5
R 5 4 3
R 5 4 1
R 5 7 5
R 5 7 6
R 5 2 9
R 5 8 3
R 5 1 5
R 5 2 5
R 5 7 4
R 5 2 6
R 5 4 4
R 5 4 2
R 5 4 8
R 5 4 7
C 5 5 5
R 5 7 8
W R 5 0 3
Copyright © 2019 LG Electronics Inc. All rights reserved.
3-7
3.3VA
R308
0 OHM(1)
NC
C322 C354 C364 C370
10uF 10uF 10uF
100nF
/10V
/10V /10V
/16V
DGND
L301 L301
L 3 0 1
F B 5 1 0
I C 3 0 1
R 3 0 8
C 5 F 1
C 5 F 2
R 5 F 1
R 5 F 2
C 3 9 2
C 3 9 1
I C 3 1 3
C 3 8 1
C 3 8 2
C 3 8 3
F B 3 1 6
F B 3 1 4
R R 5 0 3
Only for training and service purposes.
CN50
C 3 3 1
R 4 0 9
C 3 3 3
R 4 0 8
C 3 3 4
C 4 4 0