User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 36
Original 11/97
DC Voltage Checks
Check the following DC voltages with the –65 dBm modulated signal still
fed into the phone and the Service Software AMPS Troubleshooting Mode
initiated.
•The bias voltage on the AMPS RX IC (D1), pin 4 should be
approximately 4.40 V.
If not, first ensure that the phone is in the AMPS Troubleshooting Mode. Check the
VRXA supply voltage at C219, or CDCONT (N201), pin 42. If fault is found with this
DC supply then refer to the AGC Troubleshooting Manual to determine if there is a
problem with the CDCONT voltage regulators.
•Check the 1st IF gain stage V9:–
The voltage on the collector, pin 1 should be approximately 3.30 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Inspect V9, R30
and R31. Ensure that VRXAM is approximately 4.15 V at R31
The voltage on the base, pin 3 should be approximately .97 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Inspect V9, V4,
L13, L11, R4, R5, R13, R14, and R15. Ensure VRXM is at about 4.15 V at R13, and
VRXAM is about 4.15 V.
The voltage on the emitter, pins 2 and 4 should be approximately 0.25 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Inspect V9,
L14, R25, and R28.
•Check the LNA, V12:–
The voltage on the collector should be approximately 3.70 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Ensure VRXM
is at about 4.15 V at R833. Inspect V11, V12, L20, R33, R34, R38, and R833.
The voltage on the base should be .82 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Ensure VRXM
is at about 4.15 V at R833. Inspect V11, V12, L21, L22, R33, R35, and R833.
•Check the control voltages on the RF Gain Switches N701 and N702.
Pin 1 on both should be approximately 3.80 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Ensure VRXM
is at about 4.15 V at R832. Inspect N701, N702, V1, V708, R775, R777, R779,
R781, R783, R803, R830, R831, and R832.
•Check the SWAGC line at R830. It should be logic level low,
approximately .0 V.
If not, confirm that the phone is in the AMPS Troubleshooting Mode. Ensure VRXM
is at about 4.15 V at R832. Inspect V708, R765 and R830. Ohm out line from R765
to the ASIC N704 pin 94.