Nokia RM-57 Service Manual page 247

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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".
• Set TX power level to the maximum ("5" in GSM850/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 sweep time at least 2.5 seconds.
GSM850/EGSM900: Connect the probe to J7521 (test point). The RF level should be roughly
•
-15...-20 dBm.
GSM1800 or GSM1900: Connect the probe to R7512 output. The RF level should be roughly -
•
20...-30 dBm.
3.1.1.2.1 GSM850/EGSM900: Replace SAW Z7504
3.1.1.2.2 GSM1800/GSM1900: Is Vinku (N7501) output RF-signal coming to the T7502 (Balun)?
• GSM transmitter has to be active before measurements. Procedure is explained in section
"Transmitter troubleshooting". Set TX power level to the maximum ("0" in
GSM1800/GSM1900)
Measurements can be done with a spectrum analyser and an RF probe. 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 sweep time at least 2.5 seconds.
• GSM1800 or GSM1900: Connect the probe to T7502 input. There are two input ports in T7502
because the input port is balanced. The RF level should be roughly -25 dBm in both inputs.
3.1.1.2.2.1 Matching components ok?
GSM1800/GSM1900: C7575 and C7577
"BB AFC-voltage ok?"
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Appendix A: RF Troubleshooting
A-29