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Appendix A: RF Troubleshooting
3.1.1.1.9.3 Retu ok?
3.1.1.1.10 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
V)"..
3.1.1.1.10.1 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
3.1.1.1.10.1.1 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.
3.1.1.1.10.1.2 Replace Retu
3.1.1.1.10.1.3 Replace Hinku (N7500) or Vinku (N7501) or VCTCXO (G7501) or all three components
3.1.1.1.10.2 BB AFC-voltage ok?
•
See section
3.1.1.1.10.3 Replace VCTCXO G7501
3.1.1.1.11 Replace Vinku (N7501)
3.1.1.2 Is there RF-power in the GSM PA (N7502) input at all?
•
GSM transmitter has to be active before measurements. Procedure is explained in section
"Transmitter troubleshooting".
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Set TX power level to the maximum ("5" in EGSM900 and "0" in GSM1800/GSM1900)
•
Measurements can be done with a spectrum analyser and an RF probe. Remember to make correct
frequency settings to the spectrum analyser. Spectrum analyser centre frequency should be set
according the used TX 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 power should be measured during TX burst (triggering
needed). Another possibility is to use following settings: RBW = VBW = 1 MHz, Span 200 kHz and
"BB AFC-voltage ok?"
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6.5.1. "VCTCXO Output (DC Offset
A-31
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