Nokia 2626 - Cell Phone - GSM, Руководство по обслуживанию

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GSM1800 TX output power
Figure 116 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 26MHz 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 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).
RM-291
RF troubleshooting Nokia Customer Care
Issue 1 COMPANY CONFIDENTIAL Page 7 –27
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