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TB7100 Service Manual Power Supply Fault Finding 127

9 Power Supply Fault Finding

Fault-Diagnosis

Tasks

Fault diagnosis of the power-supply circuitry is divided into six tasks:

■ check inputs to SMPS

■ check 3.3 V supply

■ check linear regulators

■ check power-up

■ check power-up options

The regulators of concern in the third task are those for the 9V, 6V, 3V and

2.5V supplies.

Three Types of Fault Which of the above tasks are applicable depends on the nature of the fault:

■ radio fails to power up

■ power-up option has failed

■ external power at connector has failed

With the first fault, either the radio fails to power up immediately when

power is applied, or it fails to power up when power is applied and the

ON/OFF key is pressed. In this case carry out Task 1 to Task 3. With the

second fault, the radio powers up when the

ON/OFF key is pressed, but not

for a power-up option for which it is configured. In this case carry out

Task 4 and Task 5. With the third fault, the external power required at a

particular connector is no longer present. In this case carry out Task 6.

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