154 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 6 —
3V Power Supply
If the SMPS output and the 6V and 5V supplies are correct, the remaining
power supply to check is the 3V DC supply.
1. Measure the supply +3
V0 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
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