User Guide

NPE-4
6 - Troubleshooting PAMS Technical Documentation
Page 6-46 ãNokia Corporation. Original
VCO
The VCO is able to generate frequencies in the range of 3420 – 3840 MHz when PLL is in
function. The frequency of the VCO signal is divided by 2 or by 4 in HAGAR so it is possi-
ble to generate the frequency of all channels in EGSM and PCN (both RX and TX). Fre-
quency of the VCO is controlled by DC voltage (Vc) coming from the loop filter. Range of
the Vc when PLL is in function is 0.7 – 3.8 V. Even if PLL is not working (Vc out of range)
there is some frequency at the output of the VCO which is between 3 and 4 GHz (if the
VCO itself is ok).
Fault finding chart for PLL Synthesiser
It is important to say that power supply for VCTCXO ( VXO) is OFF only in ‘Deep Sleep
Mode’ and power supply for VCO (G630 Vcc) is OFF in ‘Sleep Mode’.
Setup with Phoenix:
Band: GSM 900
Mode: RX Continuous
Channel: 37
Spectrumanalyzer
VCO out (G630 out)
3769.6 MHz
PLL Block is functional
Yes
Yes
Oscilloscope
VCTCXO output
(G740 out)
26MHz,app.0.8Vpp
No
Oscilloscope
VCTCXO Supply
(G740 Vcc)
2.7V
Yes
PLL Synthesiser Fault finding Tree
No
Check UEM,
Software??
Phone not in function
VCTCXO is dead
No
Oscilloscope
VCO Supply
(G630 Vcc)
2.7V
Yes
Check UEM,
Software??
Phone not in function
No
Spectrumanalyzer
VCO out (G630 out)
Some signal 3-4 GHz
Yes
VCTCXO is dead
No
Check HAGAR,
Wrong writing to HAGAR
Yes
Oscilloscope
Bluetooth Clockbuffer
output (LPRFCLK_I)
(C753)
26MHz
Yes
Check Bluetooth
Clockbuffer
R750,R751,R752,
V831,C752,C753
No