One Point Repair Guide - LG SN4A Service Manual

1. NO BOOTING WHEN YOU TURN THE UNIT ON, NO MESSAGE OR "HELLO"
ON FRONT PANEL
When you turn on your set, no message on the front panel, and stand-by LED doesn't work.
1-1. IC302 System 12 VA (No 12 VA)
1-1-1. Solution
Replace MAIN board.
1-1-2. How to troubleshoot (Countermeasure)
1) Please check 25 VA of IC302 pin2 (VIN).
2) If 25 VA is abnormal, please check adapter.
3) If 25 VA is OK, but 12 VA is abnormal pin3 of IC302 (VOUT), replace MAIN board.
1-1-3. Service hint (Any picture / Remark)
25VA
FB303
DGND

ONE POINT REPAIR GUIDE

[25VA TO 12VA]
R328 100K
8
FB
7
VCC
C351 R300
6
33pF 51K
EN/SYNC
(1%)
5
BST
R335
100K
R306
DGND
VOUT = 0.792x((47K/3.3K)+1)= 12.072V
< MAIN board top view >
IC302
1
PG
2
IN
3
L302 10UH
SW
4
GND
DGND
22 C306
100nF
IC302 IC302
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3-5
12VA
PWR_GD
DGND
Only for training and service purposes.