Appendix A: RF Troubleshooting
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A-43
should be connected to the pad that can be still found from the PWB
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Typical full TX power bias currents (Icont_31 and Icont_32) should look somehow similar to figure
“Icont_31/Icont_32 (DC Offset 1.2 V)” when measured with an oscilloscope and a probe. Check
both currents.
3.1.2.3.2.1 Vinku (N7501) RB_EXT voltage ok?
•
See section
"Vinku (N7501) RB_EXT voltage ok?"
3.1.2.3.2.2 Are capacitors in GSM PA (N7502) bias lines working correctly?
EGSM: Icont_21 missing – Replace Vinku
Icont_22 missing – C7545 short-circuited?
GSM1800/GSM1900: Icont_31 missing – C7556 short-circuited?
Icont_32 missing – C7561 short-circuited?
•
Check that components are in place and solder joints are ok
•
Disconnect the power supply from the phone and use an ohmmeter to check that capacitors are
not short-circuited. If short-circuit is found replace capacitors mentioned above.
3.1.2.3.2.3 Replace Vinku (N7501) or GSM PA (N7502)
3.1.2.3.3 Replace GSM PA (N7502)
3.1.2.4 Are control voltages VC1, VC2 and VC3 coming correctly to the antenna switch (Z7503)?
•
Use “RF Controls” window in Phoenix test software to activate the GSM transmitter and to select
the wanted GSM band. Procedure is explained in section “Transmitter troubleshooting”. GSM RX
activation is described in section “GSM RX chain activation for manual measurements”.
•
Use an oscilloscope and probe to find out if antenna switch control lines are working according to
table shown below. “Hi” means that there is 2.4 – 2.8 V control voltage level in the corresponding
control line. “Lo” means levels 0 – 0.2 V. Remember to trigger the oscilloscope because control
voltages VC1, VC2 and VC3 are pulsed
•
Connect the probe to correct test points to measure VC1, VC2 and VC3 voltages (check test point
locations, see section “Test point locations). Notice: these test points are PWB pads for three non-
assembled capacitors.
3.1.2.4.1 Replace Hinku (N7500)
