Troubleshooting diagram for GSM1800 receiver
Phone in “Continuous” mode, AGC setting “12
Figure 22: GSM1800 receiver troubleshooting
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Apply –90dBm
1842.86771MHz signal
from generator to anten-
na connector
Oscilloscope at RX_I
Signal 140mVpp
DC offset 1.35V ***
Frequency 67.7kHz
Change ge-
nerator level
to –50dBm
Spectrumanalyzer
Antenna switch out-
puts,
1800 LNA out
–61 dBm
Spectrumanalyzer
Antenna Swithc input
-84 dBm
GSM1800 RX chain
functional
Oscilloscope
VR1,3...6 2.7V
Check HELGA serial
interface
(burst mode)
Check C838, C839,
L821. L 872,
C836, C837,
V801
Oscilloscope
VANT_1...3 0V
Oscilloscope
Check HELGA se-
rial interface (burst
mode)
Check HELGA
N600
Check Base-
band
* Spectrumanalyzer
reading with 1 kohm
passive probe (right val-
ue add +26 dB)
All spectrumanalyzer reading
values are measured with 1
kohm passive probe (use
tweezers to connect the
probe ground to the nearest
PWB ground). Reading value
is represented w26
dB compensation.
Check C831,
L811
Check Antenna
Switch Z800
Spectrumanalyzer
HELGA inputs
GSM 1800
–88 dBm
Check Base-
band
No
Synthesiszer trou-
bleshooting
Spectrumanalyzer
4G VCO out
3769.6MHz
∼
–30 dBm (*
Yes
Check HELGA
N500
* ** DC–level of RXI/RXQ in
continuous mode will decrease
slowly.
The original level can be resto-
red by rewriting gain set.
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3685.6
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ICQ: 343183001 QQ: 35070846 Email: [email protected]