Nokia RM-57 Service Manual page 273

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3.2.2.7.1 RX VCO operating voltage VR1 RX ok?
• GSM receiver has to be active before Hinku's VR1 voltage can be measured. Procedure is
explained in GSM RX chain activation for manual measurements.
• Measurements can be done with an oscilloscope and a probe.
• Connect the probe to C7504 (or C7505) VR1 voltage level should be 2.65 – 2.86 V. Typical value
is 2.7 V.
3.2.2.7.1.1 Hinku (N7500) regulator voltage VR1 ok?
• See section
3.2.2.7.1.2 Replace Hinku (N7500)
3.2.2.7.2 Replace RX VCO (G7500)
3.2.2.8 Is RX VCO RF-signal coming to the Hinku 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.
• Check the level of the VCO frequency in T7501 outputs. The level should be about
-25...-35 dBm in both output lines. If the signal level is correct in the input (about
-20...-30 dBm) but output level is not as expected then replace T7501.
3.2.2.8.1 Replace balun T7501
3.2.2.9 Is RX VCO frequency as expected?
• 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
"Hinku (N7500) regulator voltage VR1
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Appendix A: RF Troubleshooting
ok?"
A-55