User Guide

Figure 127 TXC signals at PCL15

Synthesizer troubleshooting

Introduction

26 MHz Reference Oscillator (VCXO)

There is only one PLL synthesizer generating Local Oscillator frequencies for both RX and TX in both bands (PCN

and EGSM). The VCO frequency is divided by 2 for PCN operation or by 4 for EGSM operation inside the RF IC.

The 26 MHz oscillator is located near the RF IC (N7600). The coarse frequency for this oscillator is set by an

external crystal (B7600). The reference oscillator is used as a reference frequency for the PLL synthesizer and

as the system clock for the Baseband. The 26 MHz signal is divided by 2 to achieve 13 MHz inside the UPP IC

(D2800).

The 26 MHz signal from the VCXO can be measured by probing R2900. The level at this point is approx. 770 mVpp.

Frequency of this oscillator is adjusted by changing the AFC-register inside the UEM IC. Example Signal Measured

at VCXO output (R2900).

RM-74

RF troubleshooting Nokia Customer Care

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