Appendix A: RF Troubleshooting
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A-33
3.1.1.2.3.1 Replace balun T7502
3.1.1.2.4 GSM1800/GSM1900: Replace attenuator R7512
3.1.1.3 Does GSM PA (N7502) transmit RF-power at all?
•
GSM transmitter has to be active before measurements. Procedure is explained in section
“Transmitter troubleshooting”.
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Set TX power level to the minimum (“19” in EGSM900 and “15” in GSM1800/GSM1900)
•
Measurements can be done with a spectrum analyser and an RF probe. Spectrum analyser centre
frequency should be set according the used TX channel (see section “Frequency mappings”).
•
Spectrum analyser RBW and VBW = 1 MHz, Span = 0, sweep time 1 ms. Notice that GSM
transmission has pulsed nature and power should be measured during TX burst (triggering
needed). Another possibility is to use following settings: RBW = VBW = 1 MHz, Span 200 kHz and
sweep time at least 2.5 seconds.
•
EGSM900: Connect the probe to J7520 (test point). The RF level should be about -16…-17 dBm.
•
GSM1800 or GSM1900: Connect the probe to J7519 (test point). The RF level should be roughly
-29…-30 dBm in both bands.
3.1.1.3.1 GSM PA (N7502) operating voltage ok?
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Measurement can be done with an oscilloscope and a probe.
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Connect the probe to C7593
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Voltage level should be 3.05 – 5.4 V. Typical value is 4.0 V
3.1.1.3.1.1 PA operating voltage VBAT_PA ok?
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Measurement can be done with an oscilloscope and a probe.
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Connect the probe to C7569 (or C7564, C7583)
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Voltage level should be 3.05 – 5.4 V. Typical value is 4.0 V.
3.1.1.3.1.1.1 Ferrite Z7500 ok?
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Check that component is in place and solder joints are ok
•
Disconnect the power supply from the phone and use an ohmmeter to check that inductor is
conducting DC.
3.1.1.3.1.2 C7593 ok?
•
Check that the component is in place and solder joints are ok
•
Disconnect the power supply from the phone and use an ohmmeter to check that the capacitor is
not short-circuited. If short-circuit is found replace the capacitor.
