Nokia RH-57 Series Troubleshooting Manual page 44

2112 (RH-57)
Troubleshooting - RF
Tuning Title
VCTCXO Frequency
Page 44
Description
The purpose of this tuning is to deter-
mine what the AFC DAC value needs to
be in order to center the VCTCXO fre-
quency. The transmitter is turned on and
no Tx baseband modulation is provided.
The carrier is then centered in frequency.
This is done to the carrier after it has
been mixed up to 836.52MHz, since it's
easier to measure the tolerance of 1ppm
at 836.52MHz than it is at 19.2MHz.
Additionally, the tone at 836.52MHz can
be measured without taking the phone
apart.
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Nokia Customer Care
Troubleshooting
1) If there is no tone, probe pin 3 of G501
for a tone at 19.2 MHz. If this is not present,
check power supplies, particularly ensure
2.7v on VCTCXO Vcc pin, pin 4 of G501. Also
check the control pin, pin 1 of G501, for a
voltage between 0.4 and 2.7v. If the volt-
ages are correct, and soldering of all G501
terminals is correct, replace G501. If 19.2
MHz tone is present but tone at
836.52 MHz is not, troubleshoot cell Tx
chain.
2) If the carrier is present but the PDM
needed to center it is outside of the +/- 150
range, or if it cannot be centered, there is a
hardware problem.
3) In the following procedure, performing
frequency centering on the RF carrier at
836.52MHz will detect frequency errors due
to the VCTCXO and supporting hardware,
which will account for the majority of the
problems, but will not detect frequency
errors due to the hardware that mixes the
VCTCXO tone at 19.2MHz up to 836.52MHz.
In order to troubleshoot this hardware, fre-
quency centering should be performed on
the 19.2MHz tone to +/- 19.2Hz on pin 3 of
G501 using a frequency counter, then the
VHF and UHF LOs should be checked.
Because this will be time-consuming and
will probably only account for a small per-
centage of the failures, it is not recom-
mended unless the situation justifies the
time spent. The VHF LO is inside the Jedi IC
(N601) and troubleshooting of the cell UHF
LO is required.
4) If the carrier can be centered but the
PDM is out of range, check the control volt-
age on pin 1 of G501. If it is 2.2v, (and pin 4
is at 2.7v, and pin 2 at 0v), then the VCTCXO
(G501) is working correctly but the circuit
that delivers the control voltage is not.
Check soldering of all G501 terminals, also
check R510, R511, C503, and D200. If the
control voltage on pin 1 of G501 is not 2.2v,
but the carrier is centered, then there is a
problem with the VCTCXO G501. If there is
2.7v on pin 4 and the soldering is correct,
then replace G501.
Company Confidential Issue 1 07/2004