User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 39
Original 11/97
CDMA Receiver Troubleshooting
Introduction
Troubleshooting the CDMA receiver of the phone is unique, but not
complicated. The following tests detail numerous ways that the CDMA
receiver functionality can be verified, all using standard test equipment.
No special CDMA signal generators or measurement equipment are
necessary to verify the CDMA receiver.
CDMA RX Quick Test with Service Software
The Service Software software package contains a quick test for the
CDMA receiver. When selected, the software prompts you to send a CW
carrier into the phone at a –65, –85, and –105 dBm signal levels, one after
the other. Hitting the ”Test” soft key prompts the software to read the
received signal level that the phone perceives digitally. A numeric value
called the RxDAC (RX D/A converter) is generated within the CDMA ASIC
to represent the signal level received. If this number falls within the range
of values listed in the Service Software window coinciding with the
respective input signal level, the CDMA RX is operating properly. For
example, for a –65 dBm input signal should provide an RxDAC value
between 480 and 520.
Note: The results of this test will only fall into the ranges stated when the RX_OFFSET
is properly tuned. With this parameter improperly tuned the resultant values will be
slightly different, but still near the stated ranges, provided that the CDMA RX module is
functional.
Set Up CDMA RX Test
To troubleshoot the CDMA receiver first remove the shields. Apply power
and service cables to the phone and turn it on. Initiate the CDMA RX
Troubleshooting Mode from Service Software. Then feed a –65 dBm
881.62 MHz unmodulated CW carrier into the phone via the RF connector
at the bottom of the phone. An unmodulated –65 dBm carrier at channel
387 will also work. A stand alone RF signal generator should do the trick,
as will a CDMA test box with this functionality. Do not forget to account for
the signal loss between the signal generator and the phone.
RX Gain Control Test
A great test to check the health of the CDMA receiver is to monitor the
gain control current to the CDAGCR IC. As the CDMA signal strength
received by the phone drops, this current increases. Naturally it is difficult
and time consuming to break the circuit and position an ammeter in the
phone to read this current. A quick way to do so is to simply read the
voltage drop across resistor R16. Position one test lead of a volt meter on
either side of this resistor and vary the RF input power at 881.62 MHz,
unmodulated CW.
The voltage drop across this resistor should resemble the values in the
table that follows. Be sure to also check the voltage drop across R17, the
RX_IREF signal. This drop should be approximately 360 mV.