Nokia RH-21 Series, Руководство по устранению неисправностей

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CCS Technical Documentation Troubleshooting
RH-21
Issue 1 05/2003 Confidential

Nokia Corporation Page 37
TX VHF VCO
The TX VHF VCO signal is used to generate transmitter Intermediate frequency. TX VHF
VCO has two fixed frequencies (361.08 MHz for lower band and 363.6 MHz for upper
band). Operating frequency is locked in Phase-locked loop and frequency is divided by
two before modulator.
Fault-finding chart for TX VHF VCO
AMPS, CH383 -> TX VHF frequency 361.08 MHz
TDMA1900, CH1000 -> TX VHF frequency 363.6 MHz
UHF Synthesizer
The UHF Synthesizer consists of an external 2GHz UHF VCO, loop filter and an integrated
PLL in the Safari RF IC. Safari T 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 2009.1MHz
to 2125.53 MHz.
In the upper band (TDMA1900), 2 GHz synthesizer frequency is fed straight to mixers. In
the lower band (AMPS and TDMA800), 2 GHZ UHF VCO frequency signal is first divided
by two inside Safari and then that divided signal is fed to mixers. The output frequency
1
START HERE
Is oscillator locked
to 361.08 MHz
or 363.6 MHz
OK!
Yes
3
Check resonator
components:
V744, C745, L746,
C747, C748
4
Check components:
C740, C741, C742, R741,
R742, R743 and
C749, C750, L750
2
Check operating
voltage:
4.75 V
at R745
Check:
L751, R745
No
OK
5
Change
cascade amplifier
N750
2.No OK
3.No
OK
4.No
OK
5.No
OK
6
Change
SAFARI
6.No
OK