Appendix A: RF Troubleshooting
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A-51
GSM1800: C7581, C7584 and L7505
GSM1900: C7523, C7525 and L7506
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Check that components are in place and solder joints are ok
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Use an ohmmeter to check that inductors are conducting DC.
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Replace matching components
3.2.2 Are RX-IQ signal waveforms and levels correct?
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Measurements can be done with an oscilloscope, a probe and signal generator.
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GSM receiver has to be active before RX IQ-signals can be measured. Procedure is explained in
section “GSM RX chain activation for manual measurements”.
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Apply –70 dBm RF signal from a signal generator to the module jig antenna connector and use
following frequencies:
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EGSM900: 942.46771 MHz (Channel 37)
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GSM1800: 1842.86771 MHz (Channel 700)
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GSM1900: 1960.06771 MHz (Channel 661)
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Remember to change correct RX channels also to Phoenix “RF controls” window!
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Check RX I and RX Q -signals in following test points:
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RX I (positive): Connect the probe to test point J7508
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RX I (negative): Connect the probe to test point J7509
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RX Q (positive): Connect the probe to test point J7510
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RX Q (negative): Connect the probe to test point J7511
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The correct RX IQ-signal is shown in figure
6.5.6 "GSM RX IQ (DC Offset 0.4 V)"
. Level of all four IQ-
signals should be about the same and RX IQ-signal frequency should be 67.71 kHz (lower detail
figure). The phase shift between I- and Q-signals should be 90 degrees.
3.2.2.1 RF operating voltage VBAT_ASIC ok?
•
See section
“RF operating voltage VBAT_ASIC ok?”
3.2.2.2 RFBUS signals ok?
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GSM receiver has to be active before RFBUS signals can be measured. Procedure is explained in
section “GSM RX chain activation for manual measurements”. Also WCDMA/GSM transmitter and
WCDMA receiver activation can be used for the measurement but then RFBUS -signals don’t
necessarily look like in figures mentioned below.
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Measurements can be performed with an oscilloscope and a probe. Check all five RF BUS signals:
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RFBUSDAT
: Connect the probe to J7504. Typical RFBUSDAT -signal is shown in figures in section
