Nokia 6680 RM-36 Service Manual page 321

Appendix A: RF Troubleshooting
WCDMA transmitter has to be active before VCP2 voltage can be measured. Procedure is explained
•
in section "Transmitter troubleshooting".
• Measurement can be done with an oscilloscope and a probe.
• Connect the probe to C2221 (or C7550).
VCP2 voltage should be about 4.75 V.
•
4.1.1.1.5.1 C7550 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 C7550 is not
short-circuited. If short-circuit is found replace the capacitor mentioned above. If this does not
help go to the next step.
4.1.1.1.5.2 Retu ok?
4.1.1.1.5.3 Vinku (N7501) ok?
4.1.1.1.6 Is there RF power in the TX VCO output at all?
• 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.
• 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. Quick VCO alive check can be done
without removing the RF shield. The RF probe should be placed as near the TX VCO output as possible
(Put the head of the probe carefully inside the VCO can through the holes of the shield). This method
can be used only to check that the TX VCO is alive. Remember to use low RF Attenuator value in the
spectrum analyser with this method.
• 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 correct VCO frequency can be found in see section "Frequency mappings". The
output level of the VCO should be about -25 dBm.
4.1.1.1.6.1 TX VCO operating voltage VREG2 (VR2) ok?
• See section 4.1.1.1.3
4.1.1.1.6.2 Replace TX VCO (G7502)
4.1.1.1.7 Is TX VCO RF-signal coming to the Vinku at all?
• 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
"Vinku (N7501) regulator voltages VREG1, VREG2
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