User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 35
Original 11/97
RSSI Check
The voltage on the ungrounded end of C13 directly represents the RSSI of
the phone. Checking this voltage will provide another quick indication of
the health of the AMPS RX module. With the –65 dBm modulated signal
mentioned above this voltage should be approximately 2.00 V.
The possibility exists that the AMPS RX is working fine with a –65 dBm
input, but has lost sensitivity and fails at lower input powers. You may
wish to perform this test at higher or lower input signal levels. The
following table details the RSSI voltage vs. input signal levels. Keep in
mind that there will be variations in the voltage levels from phone to
phone, but these are good approximations.
–45 2.32
–50 2.31
–55 2.26
–60 2.16
–65 2.00
–70 1.89
–75 1.78
–80 1.65
–85 1.54
–90 1.41
–95 1.26
–100 1.17
–105 1.07
If the RSSI DC voltages are significantly less than the ranges stated then
there is an AMPS RX sensitivity problem. A total AMPS RX failure would
yield about 1.00 V for this test for most input RF power levels. Most likely
a component or solder joint along the AMPS RX receiver path has failed.
Continue the DC Voltage Quick Checks to help determine if any of the
devices aren’t biased correctly.
If the RSSI values are significantly greater than the ranges stated then
additional RF energy above the stated input level is entering the RX path.
Check the level of the signal generator used for the test and ensure that
cable losses have been properly accounted for. Also check for any
undesired oscillations.