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Appendix A: RF Troubleshooting
both currents.
3.4.2.1 Vinku (N7501) RB_EXT voltage ok?
•
See section
3.4.2.2 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?
•
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. If this does not
help go to the next step.
3.4.2.3 Replace Vinku (N7501)
3.4.3 Are TX-IQ signals ok?
•
These current mode signals are not possible to measure, but are tested with self-tests. So if there
is no fail in 2.3 "ST_CDSP_TX_IQ_TEST" these signals should be ok. Otherwise Vinku (N7501) or
RAP3G (D2800) is faulty. Notice that it is not possible to replace RAP3G ASIC.
3.4.4 Is TX VCO signal level in the T7503 output high enough?
•
GSM transmitter has to be active before TX VCO's output level can be measured. Procedure is
explained in section "Transmitter troubleshooting".
•
Measurements can be done with a spectrum analyser and an RF probe. RBW and VBW = 1 MHz,
Span = 0, sweep time 1 ms. Spectrum analyser centre frequency should be set according the used
TX channel (see section "Frequency mappings"). Notice that GSM transmission has pulsed nature
and VCO output 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.
Check the level of the VCO frequency in T7503 outputs. The level should be about -30...-35 dBm in
•
both output lines during GSM TX burst. If the signal level is correct in the input (about -25 dBm)
but output level is not as expected then replace T7503. VCO shield has to be removed before
measurement. Remember to solder the shield back after the phone repairing.
3.4.4.1 TX VCO G7502 output level high enough?
•
GSM transmitter has to be active before TX VCO's output frequency and output level can be
measured. Procedure is explained in section "Transmitter troubleshooting".
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").
"Vinku (N7501) RB_EXT voltage ok?"
Icont_32 missing – C7561 short-circuited?
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Troubleshooting
