Vco; Troubleshooting Chart For Pll Synthesizer - Nokia RH-29 Series Manual

RH-29
6b - RF Troubleshooting
The VCXO is fine tuned by programming the AFC value via the serial bus of Mjoelner. The
necessary AFC value is written into the RefOSCAFC register in Mjoelner.

VCO

The VCO is able to generate frequencies in the range from 3420MHz to 3840MHz when
PLL is in function. The frequency of the VCO signal is divided by 2 or by 4 in Mjoelner RF-
ASIC. So it is possible to generate the frequency of all channels in GSM900 and
GSM1800 (both RX and TX). Frequency of the VCO is controlled by DC voltage (Vc) com-
ing from the PLL loop filter. Range of Vc when PLL is in function is 0.7V– 3.8V. Typical
tuning sensitivity of the VCO is 250MHz/V. Even if PLL is not working (Vc out of range)
there is a frequency at the output of the VCO, which is between 3 and 4 GHz (if the VCO
itself is ok).

troubleshooting chart for PLL Synthesizer

Set up Phoenix RF Controls
900
Band: GSM 900
Mode: RX Continuous
37
Channel: 37 190
YES
Check T702
Balanced O/P.
Signal same?
YES
Change Channel
Check T702 I/P.
124.
to 975. Does LO
LO Present?
change frequency?
YES
YES NO
Change
T702
PLL is working
It is important to say that power supply for VCXO (VR3) is only switched 'OFF' in the so-
called 'Deep Sleep Mode' and power supply for VCO (G701 VR7) is switched 'OFF' in so-
called 'Sleep Mode'.
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START
Is LO@ Check VCO Out.
YES
3.77 GHz Is LO visible?
3769.6MHz
NO
YES
NO
YES NO
Does the VC
Vge change
NO
when you change
channels?
Change
R731
YES
Check Loop Filter
Components. OK?
NO
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Company Confidential
Nokia Customer Care
KEY
Test with
Test with
Spectrum
Oscilloscope
Analyzer
Check VR7 VCO
NO
Side of R730.
Vge OK?
YES
Replace G701
Check Mjoelner Voltage Supplies
VR1A, VIO, VR3, VREF1. OK?
YES
Replace Mjoelner
Replace Faulty Loop
Filter Components
End
Check /
Inspect
Action
NO
NO
Check VR7 J618.
Vge OK?
NO YES
Refer to BB Change
R730
Fault Finding
Issue 1 05/2004