Tait TB7100, Service Manual

Page: 152 / 370

154 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 6 —
3V Power Supply
If the SMPS output and the 6 V and 5 V supplies are correct, the remaining
power supply to check is the 3 V DC supply.
1. Measure the supply
+3
V
0
AN
at pins 7 and 15 of IC503
(see Figure 11.2 ).
2. If the voltage is correct, go to “Phase-locked Loop” on page 155 .
If it is not, go to Step 3 .
3. Check the supply at L506 (see Figure 11.2 ). The measurement
point is the via shown in the figure.
4. If the voltage is correct, go to Step 5 . If it is not, the 3 V regulator
IC603 is suspect; go to Task 3 of “Power Supply Fault Finding” on
page 132 .
5. Check the components in the path from L506 to IC503. Also check
IC503; if necessary, replace IC503 (see
Figure 11.2 ).
6. If a fault is found, repair the circuit, confirm the removal of the fault,
and go to
“Final Tasks” on page 123 . If the repair failed or no fault
could be found, replace the main-board assembly and go to “Final
Tasks” on page 123 .
pins 7 and 15 of IC503: 2.9
±
0.3V DC
L506: 2.9
±
0.3V DC