User Guide

NSW-4
Disassembly & Troubleshooting
PAMS Technical Documentation
Page 43
Issue 1 Final Draft
08/00
 Nokia Mobile Phones Ltd.
VHF VCO
The VHF VCO signal is used to generate transmitter Intermediate fre-
quencies. The VHF VCO has two fixed frequencies. Operating frequency
is locked in Phase locked Loop, which is controlled by baseband.
Because the oscillator has two frequencies, it has also two different
switching modes. These modes are controlled by a BAND–signal. In
AMPS and TDMA800 modes the VHF frequency is 322.38 MHz and log-
ical level of BAND–signal is “HIGH”. In TDMA1900 mode a higher inter-
mediate frequency is needed, so the operating frequency is increased to
392.46 MHz. The BAND– signal is set to logical level “Zero”.
The VHF VCO output signal is fed to EROTUS LO–pin VV_in. Inside the
EROTUS, the signal is divided for the Phase detector and TX parts. Be-
fore injection to the I/Q–modulator, the frequency is divided by 2 .
Is oscillator
locked ?
N
Check EROTUS (N700)
(SCLK):2.8V
(SDATA):2.8V
(SENA1):2.8V
SENA is 0 during SCLK
and SDATA
OK
Check oscillator
output level
at C744
P:
Check N770
Note!
Note!
SENA1 = EROTUS PLL
SENA2 = 2G PLL (N870, pin 13)
Y
Y
N
Check PD1 at
C790
V=1–2 (LB)
=2.8–3.8 V (HB)
Y
Y
N
Change N770
Note!
Check all solderings and
missing components
CHANGE
EROTUS!
Note!
Check all components and soldering
The Oscillator is locked, when
the frequency is stable.
N
Change V723
Note!
Check all solderings and
missing components