PAMS Technical Documentation
Troubleshooting Instructions
NHM-8NX
Issue 1 05/02
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Nokia Corporation
Page 41
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
Figure 21: PLL fault finding chart
From Phoenix chose:
File
> Choose Product > NHM-8NX
Mainenance
> Testing > RF Controls >
GSM1800 > RX > Continuous > Ch 700
Spectrum Analyzer:
Measure
VCO frequency at R656
3685.6MHz
Oscilloscope:
Measure
VCXO Power Supply at C620
2.7 V
Check
UEM, Software??
Phone not in function
PLL block functional
Oscilloscope:
Measure
VCXO output
On (R425) 26 MHz,
Approx. 700mVpp
VCXO is not functional
Check
Crystal B600
Oscilloscope:
Measure
VCO Power Supply
(R656)
2,7 V
Phone not in function
Check
UEM, Software??
Oscilloscope:
Measure
PLL Power Supply
C614 & C634
Both 2,7 V
Phone not in function
Check
UEM, Software??
Oscilloscope:
Measure
V
CP
Supply C616
4,7 V
Phone not in function
Check
R603, UEM, Software??
Spectrum Analyzer:
Measure
VCO output (R656)
Some signal between
3 and 4 GHz
VCO G600 is not functional
Oscilloscope:
Measure
Control Voltage C641
between 0.5 and 4.0 V
Check
Loopfilter R618,R619,
C639-C641
Check
Mjoelner N600,
UPP D400,
RFBusClk J608,
RFBusDA J610,
RFBusX j609
& Reset_Mjoel
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes