Tait TB7100 - 15 CODEC and Audio Fault Finding

TB7100 Service Manual CODEC and Audio Fault Finding 343
© Tait Electronics Limited October 2005
15 CODEC and Audio Fault Finding
Fault Conditions This section covers the diagnosis of faults in the CODEC and audio
circuitry. There are five conditions that indicate a possible fault in the
circuitry:
■ no speaker audio or speaker audio is distorted
■ no speaker audio at auxiliary connector
■ receiver does not operate
■ no transmit modulation or modulation is distorted
■ no transmit modulation despite modulation at auxiliary connector
In the first
case regarding the speaker audio, the green STATUS LED will be
operating correctly and all unmute criteria will be satisfied. In the second
case the receiver will be operating normally. In the third
case the assumption
is that the receiver and power-supply circuitry were checked and no faults
were found. In the fourth
case regarding the transmit modulation, the radio
will be transmitting the correct amount of RF power. In the fifth
case the
transmitter will be operating normally.
Fault-Diagnosis
Procedures
The procedures for diagnosing the above faults are given below in the
following sections. In each case, however, first carry out the tasks of “Power
Supplies” on page 344. Also note that the conditions concerning the
auxiliary connector can both occur at the same time. In this case carry out
both “No Speaker Audio at Auxiliary Connector” on page 354 and “Faulty
Modulation Using Auxiliary Connector” on page 366.
CCTM commands The CCTM commands required in this section are listed in Table 15.1.
Full details of the commands are given in “Computer-Controlled Test
Mode (CCTM)” on page 91.
Table 15.1 CCTM commands required for the diagnosis of faults in the CODEC and audio circuitry
Command Description
21
32
33
110 x
323 x y
324 x y
400 x
Unmute received audio
Set radio in receive mode
Set radio in transmit mode
Set level x (in range 0 to 255) of audio volume
Generate audio tone
AUD TAP IN at tap point x of tap type y
Output audio signal at tap point x of tap type y to
AUD TAP OUT
Select channel with channel number x