Figure 78 TXC signals at PCL15Synthesizer troubleshootingIntroduction26 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 theMjoelner IC.The 26MHz oscillator is located near the Mjoelner IC. (N7600). The coarse frequency for this oscillator is setby an external crystal (B7600). The reference oscillator is used as a reference frequency for the PLL synthesizerand as the system clock for the Baseband. The 26MHz signal is divided by 2 to achieve 13MHz inside the UPPIC (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. ExampleSignal Measured at VCXO output (R2900).RM-298; RM-299RF Troubleshooting InstructionsIssue 1 COMPANY CONFIDENTIAL Page 4 –45Copyright © 2007 Nokia. All rights reserved.
