User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 46
Original 11/97
• If the signal comes up, but is very much off frequency (more than a few
kHz) or is drifting around then the one or both of the PLLs is not locked.
Proceed to the section titled Testing and Troubleshooting for Synthesizer
Lock Error.
• If no signal is seen then it is possible that the transmitter is not working.
If the noise floor rose when you initiated the test, then it is likely that the
transmitter is working, but it has no signal to amplify. This would indicated
a faulty synthesizer. To rule out synthesizer error, proceed to the next
Service Software synthesizer test, the Receiver Approach. Performing the
DC Voltage Checks would also be advised.
Quick Check with Service Software – Receiver Approach
Another way to determine if both synthesizers are working is to test the
AMPS and CDMA receiver with a signal fed in. This can be done from
Service Software. Perform the CDMA RX RF Quick Test followed by the
AMPS RX RF Quick Test. These tests are found in the Service Software
Test menu.
• If the phone passes the CDMA RX RF Quick Test then both synthesizers
are working
• If the phone fails the CDMA RX RF Quick Test, but passes the AMPS RX
RF Quick Test, then the 180 MHz VHF synthesizer has failed, assuming
both the AMPS and CDMA receivers work. Proceed to the DC Voltage
Checks, VHF Synthesizer portion
• If the phone fails both RX RF Quick Tests then proceed to the DC
Voltage checks section.
DC Voltage Checks – AMPS Troubleshooting Mode
Put the phone into AMPS Troubleshooting Mode. This will turn both of the
synthesizers on. The following details the node voltages for the VCTCXO,
PLL IC, VHF and UHF portions of the synthesizer. Note that these node
voltages will change slightly when the phone is operating in CDMA mode.
VCTCXO (G300)
• Check the bias on pin 4. It should be near 3.60 V.
If not, check R325, C303, and C334. Check VRXS at C207 near the CDCONT IC.
It should be approximately 4.40 V