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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.
4.1.3.1.2.4 Are components near the TX VCO ok?
C7571, R7519, R7523, C7573 and C7568 working correctly?
•
Check that components are in place and solder joints are ok
•
Disconnect the power supply from the phone and check resistors resistance values with an
ohmmeter.
•
Use an ohmmeter to check also that capacitors are not short-circuited
4.1.3.1.2.5 Replace Vinku (N7501) or TX VCO (G7502) or both
4.1.3.1.3 Replace TX VCO G7502
4.1.3.2 Is TX VCO signal level in the T7503 output high enough?
•
WCDMA 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. Spectrum analyser centre
frequency should be set according the used TX channel (see section "Frequency mappings"). RBW
and VBW = 1 MHz, Span ≤ 200 kHz.
•
Check the level of the VCO frequency in T7503 outputs. The level should be about -30...-35 dBm in
both output lines. 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.
4.1.3.2.1 TX VCO G7502 output level high enough?
•
WCDMA 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"). RBW
and VBW = 1 MHz, Span ≤ 200 kHz.
Connect the RF probe to the T7503 input. VCO shield has to be removed before measurement.
•
Remember to solder the shield back after the phone repairing.
•
Check if the frequency of the TX VCO is as expected. If the VCO signal is not found try to use wider
span setting. The output level of the VCO should be about -25 dBm.
4.1.3.2.1.1 Replace TX VCO G7502
4.1.3.2.2 Replace balun T7503
A-96
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Appendix A: RF Troubleshooting
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Troubleshooting
