TP9100 Service Manual Power Supply Fault Finding 151
© Tait Electronics Limited May 2005
Tas k 2 —
Check +3V3 SMPS
If the voltage at the TP3V3 test point does not reach 3.3V, then the
+3V3 SMPS needs to be investigated.
1. Use a multimeter to check the supply voltage to the SMPS at pin 8
of IC610 (see Figure 8.2). The voltage should be:
If it is, go to Step 4. If it is not, go to Step 2.
2. Disconnect the 7.5V external supply. Check for continuity and shorts
to ground in the path between the
BATT POS battery pin and pin 8 of
IC610 (see Figure 8.2). Locate and repair the fault.
3. Reconnect the 7.5V external supply. Confirm the removal of the
fault by measuring the voltage in Step 1.
If the voltage is correct, confirm the removal of the fault, and go to
“Final Tasks” on page 134. If it is not, the repair failed; replace the
main board and go to “Final Tasks” on page 134.
4. While turning the power/volume control on, check the enable signal
at pin 1 of IC610 (see Figure 8.2). For the radio to power up, this
voltage must exceed 2.0V DC.
If it exceeds 2.0V for at least one second, go to Step 7.
If it does not, go to Step 5.
5. When the power/volume control is turned on, 7
V5_SW should go
from 0V to 7.5V. This generates a pulse through C634 which turns
both Q606 transistors on for approximately 30ms, and charges C610
to approximately 7.5V (see Figure 8.2). Check for continuity and
shorts to ground or power in this path. Locate and repair the fault.
6. Re-measure the voltage in Step 4.
If the voltage is correct, confirm the removal of the fault, and go to
“Final Tasks” on page 134. If it is not, the repair failed; replace the
main board and go to “Final Tasks” on page 134.
7. Disconnect the external 7.5V power supply. Cut the track joining
LINK603 (see Figure 8.2). The resistance can be measured between
the pads to ensure that the link is cut. Reconnect the 7.5V external
supply and turn the power/volume control on. Measure the voltage
across C631.
If it is correct, go to Step 8. If it is not, go to Step 10.
8. There is a fault on the +3
V3 rail. Disconnect the 7.5V external supply.
To isolate further, short
LINK603 with solder and cut the track joining
LINK602. Again, measure the resistance to ensure that the link is cut.
pin 8 of IC610: approximately 7.5V DC
pin 1 of IC610: more than 2.0V DC
voltage across C631: 3.3V DC
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