User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 45
Original 11/97
Synthesizer Troubleshooting
Introduction
Troubleshooting the synthesizer is difficult because the oscillations that it
produces cannot be measured at the output of the phone. The RF signals
it generates are routed to various portions of the phone. Assuming the
receiver and transmitter are functional, indirect means of determining the
health of the synthesizer can be used. Both the transmitter and receiver
depend on the synthesizers to operate. If one of the two synthesizers is
not working it is most certain that a problem will show up in either the
transmitter, receiver, or both. The Service Software RF quick checks are
great tools for initial testing. Beyond that there are a few quick DC
voltages that can be used to quickly assess the health of the phone. If all
else fails, RF node power levels can be read.
Quick Check with Service Software – Transmitter Approach
The fastest way to determine if both synthesizers are working is to turn on
the AMPS transmitter. This can be done from Service Software from the
AMPS/Baseband test menu. The unmodulated transmit signal can then
be viewed with a spectrum analyzer or CDMA test box. This test requires
that the AMPS transmitter be functional. If the transmitter is faulty the
receiver may also be used as a means to test the synthesizer.
To set up this test, connect the RF output of the phone to a spectrum
analyzer or CDMA test box using the bottom connector. If the CDMA test
box is used it is best to make use of the spectrum analyzer function if the
box used has one. If not, the AMPS TX test functions will work. Configure
the analyzer as such:
Center Frequency: 836.52 MHz (Channel 384)
Span: 20 MHz
Ref Level: 30 dBm
Turn on the AMPS transmitter from Service Software, setting the power
level to the lowest setting, level 7. Tune to channel 384. Initiating the
AMPS Troubleshooting mode also turns on the AMPS transmitter to
channel 384. Look at the AMPS transmit signal on the spectrum analyzer.
• If the signal is a strong (greater than –10 dBm) CW carrier locked to
836.52 MHz then both synthesizers are working properly. Change the
span of the analyzer to 100 kHz and ensure that the carrier is on
frequency to within 100 Hz.
• If a signal comes up but is slightly off frequency then the reference clock,
the VCTCXO (G300) is mistuned. Proceed to the section titled Testing
and Troubleshooting for Frequency Error.