Synthesizer Troubleshooting; Introduction - Nokia 2630 RM-298 Service Manual

RM-298; RM-299
RF Troubleshooting Instructions
Figure 78 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
Mjoelner IC.
The 26MHz oscillator is located near the Mjoelner 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 26MHz signal is divided by 2 to achieve 13MHz inside the UPP
IC (D2800).
The 26MHz signal from the VCXO can be measured by probing R2900. The level at this point is approx.
770mVpp. Frequency of this oscillator is adjusted by changing the AFC-register inside the UEM IC. Example
Signal Measured at VCXO output (R2900).
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