Vco; Fault Finding Chart For Pll Synthesizer - Nokia NHM-8NX Series Troubleshooting Instructions

PAMS Technical Documentation

VCO

The VCO is generating frequencies in the range of 3420.2MHz – 3839.2 MHz when the
PLL is running. The output frequency from the VCO is led to the Local oscillator input of
the Mjoelner IC (N600), where the frequency is divided by 2 or 4 so that they can gener-
ate all channels in EGSM and PCN respectively. Frequency of the VCO is controlled by a
DC-voltage ( Vctrl ) coming from the loopfilter. The loopfilter consists of the components
R618, R619 and C639-C641. Range of the Vctrl when the PLL is running (locked) is 0.7V
– 3.8V. Even if the PLL is not in locked state (Vctrl out of range) there is some frequency
at the output of the VCO (G600) which is between 3 and 4 GHz. This is of course only
true if the VCO is working and if the VCO power supply is present (2.7V).

Fault finding chart for PLL Synthesizer

File > Choose Product > NHM-8NX
Mainenance > Testing > RF Controls >
GSM1800 > RX > Continuous > Ch 700
VCO frequency at R656
Issue 1 05/02
Figure 21: PLL fault finding chart
From Phoenix chose:
Spectrum Analyzer: Oscilloscope:
Measure
VCXO Power Supply at C620
3685.6MHz
Yes
Oscilloscope:
VCXO output
PLL block functional
On (R425) 26 MHz,
Approx. 700mVpp
Oscilloscope:
VCO Power Supply
Oscilloscope:
PLL Power Supply
C614 & C634
Both 2,7 V
Oscilloscope:
V
CP
Spectrum Analyzer:
VCO output (R656)
Some signal between
3 and 4 GHz
Oscilloscope:
Control Voltage C641
between 0.5 and 4.0 V
Mjoelner N600,
UPP D400,
RFBusClk J608,
RFBusDA J610,
RFBusX j609
& Reset_Mjoel
ãNokia Corporation
Troubleshooting Instructions
Check
Measure No
UEM, Software??
Phone not in function
2.7 V
Yes
VCXO is not functional
Measure No
Check
Crystal B600
Yes
Measure Phone not in function
No
Check
(R656) UEM, Software??
2,7 V
Yes
Measure Phone not in function
No
Check
UEM, Software??
Yes
Phone not in function
Measure No
Check
Supply C616
R603, UEM, Software??
4,7 V
Yes
Measure
No
VCO G600 is not functional
Yes
Check
Measure No
Loopfilter R618,R619,
C639-C641
Yes
Check
NHM-8NX
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