Tait TM8100 mobiles, Service Manual

Page: 172 / 620

172 Power Supply Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Task 2 —
Check 3.3V 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 7.2 ). The voltage is 3.3V
when there is no fault.
If the voltage is correct, the digital board is faulty; replace the board
and go to
“Final Tasks” on page 163 . 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
Q600
LK8 (R786)
LK7 (R787)
3V3 test point: 3.3
±
0.1 V DC