Tait TM8000 Series, Service Manual

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208 Diagnosis of Faults on Main Board TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
9.6 Transmitter
Introduction
This subsection covers the diagnosis of faults in the transmitter circuitry.
The main indication of a fault in the transmitter is a reduction in range.
This implies that the power output is wrong or too low. Another type
of fault is manifested when the radio always transmits at full power, even
if set otherwise. Regardless of the fault, the lock status should be normal.
The procedure for diagnosing transmitter faults is divided into 16 tasks.
Before beginning the fault diagnosis with Task 1, note the following
concerning can removal and transmit tests.
Can Removal and
Replacement
There are five cans shielding the bulk of the transmitter circuitry:
■
PAD TOP
■
PAF TOP
■
DIRC TOP
■
PIN TOP
■
LPF TOP
To remove any can, first remove the main-board assembly from the
chassis. In the case of the
PAD TOP
and
PAF TOP
cans, also remove the
screws securing the heat-transfer block to the PCB; then separate the
block slightly from the PCB (the RF connector limits the amount of
movement). Secure the block again before any transmit tests. Replace
all cans that have been removed only after repairing the board. (This
applies to the B1, D1, H5 and H6 bands. For certain other bands the
transmitter will not operate correctly unless all the cans are fitted.)
Transmit Tests
Observe the precautions listed in Subsection 8.1 regarding transmit tests.
In particular, always place the main-board assembly in the chassis before
a transmit test. Also ensure that the assembly is secured by at least the
two external screws and one of the internal screws. There is no need,
however, to secure the lid of the radio body. To prevent overheating,
place the radio in receive mode as soon as possible after a transmit test.
The reason for this is that the transmit timers do not function in CCTM
mode.