14.12 Ptt Faulty - Tait TM9100 Service Manual

14.12 PTT Faulty

The PTT signal from the microphone connector is connected to the FPGA
via a resistor (R25) and relayed to the radio as a digital command.
Figure 14.17 Circuit diagram of the PTT circuitry
Note
If the PTT is faulty:
1.
2.
3.
418 Fault Finding of Control Head
FP PTT
FPGA
C108
This section only describes faults to the PTT caused by the con-
trol head, which has been established during the initial servicing
tasks by means of elimination test. For fault finding of the ??? cir-
cuitry of the main board, refer to xxx on page yyy.
With no PTT switch and hookswitch operated, check whether pin 4
of J106 is 4V.
J106 pin 4: 4V
If the signal is correct, continue with step 2.
If the signal is incorrect, inspect R25 for open or shorted contacts.
Repair if necessary. Repeat step 1.
With the PTT switch operated, check whether the same 4V are
pulled to ground on the other side of R25.
If the signal is correct, continue with step 3.
R25: GND
If the signal is incorrect, inspect D106 and C108 for short-circuits.
Repair if necessary.
Verify continuity between R25 and the FPGA. Repair PCB track if
possible.
Microphone
Connector
R25
MIC PTT
4
J106
D106
TM9100 Service Manual
© Tait Electronics Limited August 2005