Synthesizer Fault Finding; General; Vctcxo; Vco - Nokia NSB-7 Series Service Manual

PAMS Technical Documentation

Synthesizer fault finding

General

To test VCO frequency properly spectrum analyzer has to be able to measure 4GHz fre-
quencies.

VCTCXO

VCTCXO signal can be measured from point VXO3 and VXO4, VXO4 is 13MHz clock signal
for BB parts and VXO3 is 26 MHz signal for Hagar) refer the results to RF measurement
points. IF 13 MHz is not present but 26 MHz is Hagar divider has a problem. IF 26 MHz is
not present VCTCXO has problem.

VCO

VCO signal can be measured at point VCO5. VCO operation can be checked also with
oscilloscope by measuring the control voltage in RX burst mode. Additional settings
should be GSM1900 mode, RX burst mode, channel 810 and monitoring channel 512.
Refer to RF measurement points.
If VCO is not operating check Vcc (points VCO1, VCO3 and VCO2) Refer to figure 9 in RF
measurement points. If supply voltages are ok VCO has problem.
Issue 1 06/00 ãNokia Mobile Phones Ltd.
Disassembly & Troubleshooting
NSB-7
Page 43