LG KG280 Service Manual - Page 47

Checking VCTCXO Circuit

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4. TROUBLE SHOOTING (1) Checking VCTCXO Circuit TEST POINT X600.4 (VCC) X600 Figure 7 CHECKING FLOW Check Pin 3. 26 MHzO.K? Refer to Graph 4-(b) No Check Pin 4. 2.75V OK? Refer to Graph 4-1(a) No X600.3 (OUT) Check U101 Yes VCTCXO Circuit is OK See next Page to check Mobile SW Yes Changing X600 CIRCUIT AFC R622 15K C647 X600 (b) 1 VCONT OUT 3 2 GND VCC 4 2V75_VVCXO (a) 1000p 26MHz C648 TG-5010LH-26M 2.2u EXSK0008101 WAVEFORM Graph 4-1(a) LGE Internal Use Only - 48 - Graph 4-1(b) Copyright © 2007 LG Electronics. Inc. All right reserved. Only for training and service purposes

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LGE Internal Use Only
Copyright © 2007 LG Electronics. Inc.
All right reserved.
Only for training and service purposes
(1) Checking VCTCXO Circuit
4. TROUBLE SHOOTING
- 48 -
Figure 7
X600.3
(OUT)
X600.4
(VCC)
X600
Check Pin 3.
Refer to Graph 4-(b)
26 MHzO.K?
No
No
VCTCXO Circuit is OK
See next Page to check
Mobile SW
VCTCXO Circuit is OK
See next Page to check
Mobile SW
Yes
Check Pin 4.
Refer to Graph 4-1(a)
2.75V OK?
No
Yes
Changing X600
Check U101
2.2u
C648
C647
1000p
2V75_VVCXO
2
GND
3
OUT
VCC
4
VCONT
1
26MHz
TG-5010LH-26M
EXSK0008101
X600
R622
15K
AFC
TEST POINT
CHECKING FLOW
CIRCUIT
WAVEFORM
Graph 4-1(a)
Graph 4-1(b)
(b)
(a)