Tait TP9100 - Page 154

154 Power Supply Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 3 —
Check +1V5 SMPS
If the voltage at the TP3V3 test point is 3.3V but the voltage at the TP1V5 does
not reach 1.5V then the +1V5 SMPS needs to be investigated.
1. Use a multimeter to check the supply to the SMPS at pin 4 and the
enable signal at pin 1 of IC606 (see Figure 8.3):
If both voltages are correct, go to Step 4. If either or both are not go
to Step 2.
2. Disconnect the 7.5V external supply. Check for continuity on the
3V3 rail to pins 1 and 4 of IC606. Locate and repair the fault.
3. Reconnect the 7.5V external supply and turn the power/volume
control on. Confirm the removal of the fault by re-measuring the
voltage in Step 1, and go to “Final Tasks” on page 134. If the voltage
is not correct, the repair failed; replace the main board and go to
“Final Tasks” on page 134.
4. Disconnect the 7.5V external supply. Cut the track joining
LINK600
(see Figure 8.3). The resistance can be measured between the pads
to ensure that the link is cut. Check the voltage across C622 (see
Figure 8.3):
If it is correct, go to Step 5. If it is not, go to Step 7.
5. There is a fault on the +1V5 rail. Disconnect the 7.5V external
supply. To isolate further, short
LINK600 out with solder and cut the
track joining
LINK601. Again measure the resistance to ensure that the
link is cut. Measure the voltage across C622 (see Figure 8.3):
If it is correct, the fault is somewhere on the rail after
LINK601. If it is
not, the fault is on the rail between the links. Locate and repair the
fault.
6. Repair
LINK600 and LINK601 (see Figure 8.3), reconnect the external
7.5V power supply and turn on the radio. If the radio powers up, go
to “Final Tasks” on page 134. If the radio fails to power up, the repair
failed; replace the main board and go to “Final Tasks” on page 134.
7. Disconnect the 7.5V external supply. Check continuity and for faults
around IC606, L601, C627, C622, R618, and R617 (see
Figure 8.3).
8. Repair
LINK600 (see Figure 8.3), reconnect the external 7.5V power
supply and turn on the radio. If the radio powers up, go to “Final
Tasks” on page 134. If the radio fails to power up, the repair failed;
replace the main board and go to “Final Tasks” on page 134.
pin 4 of IC606: 3.3V DC (supply)
pin 1 of IC606: 3.3V DC (enable)
voltage across C622: 1.5V DC
voltage across C622: 1.5V DC