Nokia 6680 RM-36 Service Manual page 305

Appendix A: RF Troubleshooting
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.
3.2.2.9.1.2.3.3 Replace Hinku (N7500) or Vinku (N7501) or both
3.2.2.9.1.2.4 Replace Hinku (N7500)
3.2.2.9.1.3 Balun T7501 ok?
• GSM receiver has to be active before RX VCO's output frequency and output level can be measured.
Procedure is explained in section "GSM RX chain activation for manual measurements".
• 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").
• Spectrum analyser RBW and VBW = 1 MHz, Span = 0, sweep time 1 ms. Notice that GSM
transmission has pulsed nature and VCO output power should be measured during RX is active
(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 T7501 outputs. The level should be about -25...-35 dBm in
both output lines. If the signal level is correct in the input (about -20...-30 dBm) but output level is
not as expected then replace T7501.
3.2.2.9.1.4 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
•
3.2.2.9.1.5 Replace Hinku (N7500) or RX VCO (G7500) or both
3.2.2.9.2 Replace RX VCO G7500
3.2.2.10 Is RX VCO signal level in the T7501 output high enough?
• GSM receiver has to be active before RX VCO's output frequency and output level can be measured.
Procedure is explained in section "GSM RX chain activation for manual measurements".
• 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").
Spectrum analyser RBW and VBW = 1 MHz, Span = 0, sweep time 1 ms. Notice that GSM
•
transmission has pulsed nature and VCO output power should be measured during RX is active
(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 T7501 outputs. The level should be about -25...-35 dBm in
Company Confidential
Copyright © 2005 Nokia. All rights reserved
Nokia Customer Care
A-59