CCS Technical Documentation
Troubleshooting
RH-13
Issue 1 11/02
ã
Nokia Corporation
Page 69
UHF SYNTHESIZER
The UHF synthesizer consists of a external 2GHz UHF VCO, loop filter and integrated PLL
in Safari RF-IC. Safari GTE IC contains stages like counters, prescaler, divider by two,
phase and frequency comparator and a charge pump circuit which allows two opera-
tional modes analog and digital. The UHF VCO Oscillation frequency is from 2004.8 MHz
to 2124 MHz
In upper band (TDMA1900 &GSM1900) 2 GHz synthesizer frequency is fed straight to
mixers. In lower band case (AMPS, TDMA800 and GSM850) 2 GHZ UHF VCO frequency
signal is first divided by 2 inside SAFARI and then that divided signal is fed to mixers. The
output frequency of the VCO depends on the DC-control voltage which is controlled by
PLL-circuit inside SAFARI.
Figure 49: Fault finding chart for UHF SYNTHESIZER.
START HERE!
Is frequency locked?
2004.8 - 2124
MHz
Is EVM OK?
1
Check
loopfilter
components
Yes
No
OK
Change
SAFARI N801
No
Check VCO
operatig
voltage:
2.78 V
1.
No
OK!
YES
Check resistor
R811
No
OK
OK
Low band:
Is divided
signal OK?
low
band
Yes
No
Check loopfilter
components and
balun T801,
C863,C862,C861,
C860,R806,
R815,R814,R813
2. No
OK
4. No
Change
VCO G802
3.
No
OK