Appendix A: RF Troubleshooting
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Company Confidential
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2005 Nokia. All rights reserved
A-39
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Check that the component is in place and solder joints are ok
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Disconnect the power supply from the phone and check with an ohmmeter that C7595 is not
short-circuited.
3.1.2.1.5.2 Replace Vinku (N7501)
3.1.2.1.6 Are components in GSM power control loop in place and working ok?
R7516 and C7559
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Disconnect the power supply from the phone and use an ohmmeter to check that C7559 is not
short-circuited. If short-circuit is found replace the capacitor.
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Check R7516 resistance value with an ohmmeter and replace resistor if needed.
3.1.2.1.7 Is TX VCO signal level in the T7503 output high enough?
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GSM transmitter has to be active before TX VCO’s output level can be measured. Procedure is
explained in section “Transmitter troubleshooting”.
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Measurements can be done with a spectrum analyser and an RF probe. RBW and VBW = 1 MHz,
Span = 0, sweep time 1 ms. Spectrum analyser centre frequency should be set according the used
TX channel (see section “Frequency mappings”). Notice that GSM transmission has pulsed nature
and VCO output 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.
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Check the level of the VCO frequency in T7503 outputs. The level should be about -30…-35 dBm in
both output lines during GSM TX burst. If the signal level is correct in the input (about -25 dBm)
but output level is not as expected then replace T7503. VCO shield has to be removed before
measurement. Remember to solder the shield back after the phone repairing.
3.1.2.1.7.1 TX VCO G7502 output level high enough?
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GSM transmitter has to be active before TX VCO’s output frequency and output level can be
measured. Procedure is explained in section “Transmitter troubleshooting”.
•
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 VCO output 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.
•
Connect the RF probe to the T7503 input. VCO shield has to be removed before measurement.
Remember to solder the shield back after the phone repairing.
•
Check if the frequency of the TX VCO is as expected. If the VCO signal is not found try to use wider
span setting. The output level of the VCO should be about -25 dBm during GSM TX burst.
3.1.2.1.7.1.1 Replace TX VCO G7502
