Check 3.3 V Supply - Tait TM9100 Service Manual

Figure 7.2 Important components of the power-supply circuitry (top side),
including 9V regulator IC601
If the inputs at pin 5 and pin 7 of IC602 in the SMPS circuitry are correct,
Task 2 —

Check 3.3 V Supply

but the radio fails to power up, then the 3.3V DC supply needs to be
investigated.
1.
156 Power Supply Fault Finding
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
/ key depressed, measure the supply at the 3
ON OFF
the corner of the digital board (see
when there is no fault.
3V3 test point: 3.3 ± 0.1 V DC
If the voltage is correct, the digital board is faulty; replace the main-
board assembly and go to
not correct, go to Step 2.
V
Figure 7.2). The voltage is 3.3V
"Final Tasks" on page 147. If the voltage is
© Tait Electronics Limited August 2005
3 test point near
TM9100 Service Manual