LG U300 Service Manual page 86

4.6.1 Checking VCO Block
TP5
TP1
GSM_PA_EN
IN
1
G1 O1
2
3
R110
24
R115
200
R116
150
+VPWR
MQW5V0C869M
C605
10
0.01u R118
220
1
R121 5
15
8
R123
12
270
13
14
GSM_PA_RAMP
GSM/DCS/PCS
TP6
Test Point (TXVCO Level)
TP2
TP4
925-960 MHz
L119 9.1nH
L120 10nH
R111
C124 C125 C126
(PPS)
82
120p
1000p 22n
(2012)
R117
47
U103
3
VC VB
9 R119 100
OUT_GSM SW1
11
OUT_DCSPCS SW2
C140 C133
2
33p 10u
GND5 GND1
4
GND6 GND2 C142
C141
6
15p
GND7 GND3
0.1u
7
GND8 GND4
Schematic of RF TXVCO
- 87 -
4. TROUBLE SHOOTING
VREG_RFTX_2.85V
C129
0.1u
C118
10u
FB100
VREG_RFTX_2.85V
GSM_TX_VCO_0_EN_N
R120 100
GSM_TX_VCO_1_EN_N
C143
15p
VREG_MSMP_2.7V
TP3
GSM1800_INN
34
GSM1800_INP
35
VDDA10
36
GSM900_INP R
37
GSM900_INN
38
VDDA11
39
TX_MOD_CP
40
VDDA12
41
TX_VCO_FB
42
C119
R114
82p
C130
51
100p
R122
51
C144 C145 C146
0.1uF 0.01u 22p
SBCK
SBDT
SBST