14.12 Ptt Faulty - Tait TM8100 mobiles Service Manual

14.12 PTT Faulty

444 Fault Finding of Control Head with Graphical Display
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
FPGA
Note
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.
If the PTT is faulty:
1. 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
If the signal is incorrect, inspect R25 for open or shorted contacts.
Repair if necessary. Repeat
2. 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
R25: GND
If the signal is incorrect, inspect D106 and C108 for short-circuits.
Repair if necessary.
3. Verify continuity between R25 and the FPGA. Repair PCB track if
possible.
R25
FP PTT
C108 D106
Step
Step 1.
Step
© Tait Electronics Limited November 2007
Microphone
Connector
MIC PTT
4
J106
2.
3.
TM8100/TM8200 Service Manual