Tait TB7100, Service Manual

Page: 128 / 370

130 Power Supply Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 2 —
Check 3.3 V Supply
If the inputs at pin 5 and pin 7 of IC602 in the SMPS circuitry are correct,
but the radio fails to power up, then the 3.3V DC supply needs to be
investigated.
1. First determine as follows if a fault on the digital board is affecting the
supply or preventing the radio from powering up: While keeping the
ON
/
OFF
key depressed, measure the supply at the
3
V
3
test point near
the corner of the digital board (see Figure 9.2 ). The voltage is 3.3 V
when there is no fault.
If the voltage is correct, the digital board is faulty; replace the main-
board assembly and go to
“Final Tasks” on page 123 . If the voltage is
not correct, go to Step 2 .
Figure 9.2 Important components of the power-supply circuitry (top side),
including 9V regulator IC601
3V3 test point
Q600
3V3 test point: 3.3
±
0.1 V DC