Nokia 6680 RM-36 Service Manual page 302

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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.
• Connect the RF probe to the T7501 input.
• Check if the frequency of the RX 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 -20...-30 dBm.
3.2.2.7.1 RX VCO operating voltage VR1 RX ok?
• GSM receiver has to be active before Hinku's VR1 voltage can be measured. Procedure is explained
in GSM RX chain activation for manual measurements.
• Measurements can be done with an oscilloscope and a probe.
• Connect the probe to C7504 (or C7505) VR1 voltage level should be 2.65 – 2.86 V. Typical value is
2.7 V.
3.2.2.7.1.1 Hinku (N7500) regulator voltage VR1 ok?
• See section
3.2.2.7.1.2 Replace Hinku (N7500)
3.2.2.7.2 Replace RX VCO (G7500)
3.2.2.8 Is RX VCO RF-signal coming to the Hinku at all?
• 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.
3.2.2.8.1 Replace balun T7501
3.2.2.9 Is RX VCO frequency as expected?
• GSM receiver has to be active before RX VCO's output frequency and output level can be measured.
A-56
"Hinku (N7500) regulator voltage VR1
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Appendix A: RF Troubleshooting
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