Nokia RM-57 Service Manual page 276

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
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