Nokia 6680 RM-36 Service Manual page 351

Appendix A: RF Troubleshooting
change if RX channel is changed. VC is lower on lower channels and higher if higher channel
numbers are used.
4.2.4.8.1.1 VCP1-voltage ok?
• WCDMA receiver has to be active before VCP1 voltage can be measured. Procedure is explained in
section "Receiver troubleshooting".
Measurement can be done with an oscilloscope and a probe.
•
• Connect the probe to C7507.
• VCP1 voltage should be about 4.75 V.
4.2.4.8.1.1.1 C7507 and C2222 working properly?
• Check that the components are in place and solder joints are ok
• Disconnect the power supply from the phone and use an ohmmeter to check that C507 and C2222
are not short-circuited.
4.2.4.8.1.1.2 Retu ok?
4.2.4.8.1.1.3 Hinku (N7500) ok?
4.2.4.8.1.2 Balun T7501 ok?
• WCDMA receiver has to be active before RX VCO's output frequency and output level can be
measured. Procedure is explained in section "Receiver troubleshooting".
• Measurements can be done with a spectrum analyser and an RF probe. Spectrum analyser centre
frequency should be set according the used RX channel (see section "Frequency mappings"). RBW
and VBW = 1 MHz, Span ≤ 200 kHz.
• Check the level of the VCO frequency in T7501 outputs. The level should be about -25...-35 dBm. If
the signal level is correct in the input (about -20...-30 dBm) but output level is not as expected
then replace T7501.
4.2.4.8.1.3 Are components near the RX VCO ok?
R7501, C7516, R7505, C7524 and C7522 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
4.2.4.8.1.4 Replace Hinku (N7500) or RX VCO (G7500) or both
4.2.4.8.2 Replace RX VCO G7500
4.2.4.9 Is RX VCO signal level in the T7501 output high enough?
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