LG CU920 - GSM Block Troubleshooting Steps

4.8.2 Checking PAM Block
1. TP1 : GSM_PA_RAMP
→ Power Amp Gain Control. typically, 0.2V < Vramp < 1.6V
2. TP2 : GSM_PA_EN
→ Power Amp Enable (Power ON : higher than 1.25V, Power OFF : lower than 0.4V)
3. TP3 : GSM_PA_BAND
→ Power Amp Band Selection Control
(GSM Mode : -0.2V < VBS < 0.4V, DCS/PCS Mode : 1.25V < VBS < 3.0V)
4. TP4 : +VPWR
→ PAM Supply Voltage Vcc higher than 3.0V
5. TP5 : GSM_SAW_SW_MODE
→ High : G900, Low : G850
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Only for training and service purposes
4. TROUBLE SHOOTING
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TP1
TP4
TP5
TP2
TP3
Fig. 4.8.2.1 Test point of the GSM PAM Block
7.75dB
HIGH
remain LOW when not transmitting
EGSM
GSM850
LOW
82
R115
51
R119
LMSM32AA-533
GND1
2 3
GND2 GND3
4 6
GND4 GND5
8
1
RFINRFOUT
5
7
VC
FL101
110
R120
C143
NA
200
R122
68p
C128
C132
33p
12
1
TX_EN
VAPC
6 5
VBATT
PGND15 PGND16
32
PGND17
33 34
PGND18
35
PGND19 PGND2
18
PGND20
36 19
PGND3
20
PGND4 PGND5
21 22
PGND6
23
PGND7 PGND8
24
PGND9
25
RSVD1
4
RSVD2
8
RSVD3
BS
2
DCS_PCS_IN
DCS_PCS_OUT
16
10
GND1
11
GND2 GND3
13 14
GND4 GND5
15
GSM_IN
7
GSM_OUT
9
PGND1
17 26
PGND10
27
PGND11
28
PGND12 PGND13
29
PGND14
30 31
U101
SKY77329
3
2.2KR113
33u
C129
R121
110
82
R116
R117
82
GSM_PA_EN
+VPWR
GSM_PA_RAMP
DCS_PCS_TX
GSM_PA_BAND
GSM_TX
GSM_SAW_SW_MODE
Fig. 4.8.2.2 Schematic of the GSM PAM Block
TP1
TP4
TP2
TP5
TP3