Nokia RM-57, Руководство по обслуживанию

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Nokia Customer Care Appendix A: RF Troubleshooting
Company Confidential
Copyright © 2005 Nokia. All rights reserved
A-59
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.
3.2.2.10.1 RX VCO G7500 output level 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.
• 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. Output level of the VCO should be about -20…-30 dBm.
3.2.2.10.1.1 Replace RX VCO G7500
3.2.2.10.2 Replace balun T7501
3.2.2.11 VCTCXO frequency and output level correct?
• Measurement can be done with an oscilloscope and a probe.
• Connect the probe to C7529 (or C7582)
• The frequency of the VCTCXO should be quite exactly 38.4 MHz and level about 0.5 - 0.9 Vpp.
Example of the correct VCTCXO output signal is presented in figure
4.6.1 "VCTCXO Output (DC
Offset 1.24 V)" .
3.2.2.11.1 VXO-voltage ok? (=Vdig).
• Measurement can be done with an oscilloscope and a probe
• Connect the probe to C7560 (or C7526, C7513)
• VXO-voltage should be about 2.5 V