Nokia 6680 RM-36 Service Manual page 278

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sweep time at least 2.5 seconds.
• 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 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
• Check that components are in place and solder joints are ok
• GSM1800 and GSM1900: Disconnect the power supply from the phone and use an ohmmeter to
check that capacitors C7575 and C7577 are not short-circuited. If short-circuit is found replace the
faulty capacitor.
3.1.1.2.3 GSM1800/GSM1900: Is there RF power in the balun (T7502) output at all?
• 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. 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.
• GSM1800 or GSM1900: Connect the probe to R7512 input. The RF level should be roughly -20...-
30 dBm.
A-32
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Appendix A: RF Troubleshooting