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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
1.24
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
3.2.2.11.1.1 C7560, C7513, C7526 and C2214 ok?
•
Check that components are in place and solder joints are ok
•
Disconnect the power supply from the phone and use an ohmmeter to find out if the VXO-line is
short-circuited to the ground. If short-circuit is found replace C7560, C7513, C7526 and C2214. If
replacing does not help then go to the next steps.
A-60
V)".
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Appendix A: RF Troubleshooting
6.5.1 "VCTCXO Output (DC Offset
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