Tait TB7100, Service Manual

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TB7100 Service Manual Power Supply Fault Finding 127
© Tait Electronics Limited October 2005
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 9 V, 6 V, 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 .