Nokia RM-57 Service Manual page 272

Appendix A: RF Troubleshooting
3.2.2.6.1.2 Replace Retu
3.2.2.6.1.3 Replace Hinku (N7500) or Vinku (N7501) or VCTCXO (G7501) or all three components
3.2.2.6.2 BB AFC-voltage ok?
• Measurement can be done with an oscilloscope and a probe
• Connect the probe to R7509 (or C7533)
• AFC-voltage may vary between 0.1 - 2.3 V. Typical value is 1.2 V. Phoenix "RF Controls" tool can
be used to change the AFC value. Voltage level should be about 0.1 V with AFC value -1024
and about 2.3 V with AFC value 1023.
3.2.2.6.2.1 Low pass filter components R7509 and C7533 ok?
• Check that components are in place and solder joints are ok
• Disconnect the power supply from the phone and check R7509 resistance value with an
ohmmeter.
• Use an ohmmeter to find out also if the AFC-line is short-circuited to the ground. If short-
circuit is found replace C7533. If this does not help then go to the next steps.
3.2.2.6.2.2 VCTCXO ok?
Remove R7509. If AFC-voltage is correct after removing then replace faulty VCTCXO G7501 and
•
solder R7509 (new component) back to the PWB
3.2.2.6.2.3 Replace Retu
3.2.2.6.3 Replace VCTCXO G7501
3.2.2.7 Is there RF power in the RX VCO output at all?
• 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. The output level of the VCO should be about -20...-30 dBm.
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