156 Power Supply Fault Finding TM9100 Service Manual
© Tait Electronics Limited August 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 3V3 test point near
the corner of the digital board (see Figure 7.2). The voltage is 3.3V
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 147. If the voltage is
not correct, go to Step 2.
Figure 7.2 Important components of the power-supply circuitry (top side),
including 9V regulator IC601
3V3 test point: 3.3 ± 0.1 V DC
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