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418 Fault Finding of Control Head 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.

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. For fault finding of the ??? cir-

cuitry of the main board, refer to xxx on page yyy.

If the PTT is faulty:

1. With no PTT switch and hookswitch operated, check whether pin 4

of J106 is 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.

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 step 3.

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.

Figure 14.17 Circuit diagram of the PTT circuitry

J106 pin 4: 4V

R25: GND

J106

Microphone

Connector

FPGA

FP PTT

R25

MIC PTT

C108

D106

Tait TM9100 Service Manual

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