LG RN7 - Page 34

3-7
Copyright © 2020 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
ONE POINT REPAIR GUIDE
NO BOOTING IN USB FUNCTION
After you turn on power key and displayed message in the following order (HELLO  VOL XX  USB)
on VFD, it will not display other message on VFD, and it will not boot-up normally.
4-2. CRYSTAL (X500)
4-2-1. Solution
Replace MAIN board.
4-2-2. How to troubleshoot (Countermeasure)
1) If 3.3 V & 1.2 V is normal, check reset ‘High’ of IC501 pin T12 on MAIN board.
 If CHIP_RESET isn’t high, check the IC505.
2) If CHIP_RESET is high, check the soldering status of 24 MHz crystal (X500).
3) If the crystal(X500) doesn’t oscillate, check R5B4, R5B6, C5B2, C5B5 around crystal(X500).
 If there’s no defective component, then replace X500.
4-2-3. Service hint (Any picture / Remark)
S
35791
2468
11 13 17
10 12 14 16
15
A
B
C
D
E
F
G
H
J
K
L
M
N
P
R
T
U
F
T_TX
R5B4
R5B5
R5B6
5B7 5B8
RA501
RA502
RA503
RA504
C5B2
C5B4
C5B5
ZD501
C5E2
C5E3
ZD505
ZD506
SF_CS
FL500
C5B11 C5B14
C5B18
C5B23
C5B24
R508
C5B34
15
R5D10
21
2
SF_MI
S
C5B60
45
X500
X501
R5B51
R5B53
R5B1
R5B56
R5B102
R5B104
R5B106
R5B107
R5B60
R5B61
R5B64
R5B65
R
5B69
R
5B70
R5B72
R5B73
R5B74R5B75
R5B94
RX
R5B95
R5B98
R5B
9
R596
IC501
XX
X
I
I
X
X
O
O
X500
< Signal waveform >
< MAIN board top view >
IC501
IC501
X500
X500