Ericsson LBI-38953 Maintenance Manual page 8

LBI-38953
SYMPTOMS AND CHECKS (CONTINUED)
SYMPTOMS
Distorted TX Audio
Transmitter Off
Frequency
Calls Processed
Incorrectly
Improper Direct Mode
8
Check grounding between all Boards and the casting.
Check the TX MOD input to the RF Board. If distorted, a faulty Audio Board is likely.
Check the mute commands. If incorrect a faulty Logic Board is likely.
If the tones are distorted, check the tone generation circuitry on the Logic Board.
Suspect the RF board. Refer to "Frequency Set" procedure in the Transmitter Alignment section
of this manual. Check the synthesizer load command. If the load command is wrong, a faulty
Logic Board is likely.
Check personality PROM programming. Check for proper TX and RX operation. Refer to TX
and RX Verification Procedures.
If verification OK, determine if the problem is in the transmit or receive circuit.
RX decode check: Use test mode Decode Test (FCN 13). Modulate the generator with the
correct tone sequence and busy tone. If the test fails, check the limited data output from the
Audio Board. If the data is present, the Logic Board may be faulty, If the data is not present,
the Audio Board may be faulty.
TX encode check: Use FCN 08 for the encode test. If the test fails, the Audio or Logic Board
may be faulty. Look for the proper tones to the Audio Board and proper unmute commands
from the Logic Board. If all inputs are correct, the Logic Board may be faulty.
TX/RX/Encode/Decode OK: Check for proper synthesizer switching time. Use FCN 10 for the
test. If the switching time is incorrect, the RF board may be faulty.
Use the FCN 21 command and check the BANDSWITCH LINE. If the command is correct,
the RF Board may be faulty. If the command is incorrect, the Logic Board may be faulty.
The radio must be equipped with talk-around option for direct mode operation to
work properly. DAMAGE to the radio may occur if the radio is placed in talk-around
transmit mode without the talk-around option board installed.
CHECKS
CAUTION