158 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 9 —
DIG SYN EN Line
If the supply for the charge pump and the reference frequency are correct,
check the
DIG SYN EN line input.
1. Check the
DIG SYN EN line at pin 10 of IC503 (see Figure 11.2).
Enter the CCTM command 334 0 to switch off the synthesizer, and
measure the voltage at pin 10.
2. Enter the command 334 1 to switch on the synthesizer, and measure
the voltage again.
3. If the voltages measured in Step 1 and Step 2 are correct, go to
Task 10
. If they are not, go to Step 4.
4. Remove R104 (see Figure 11.6) and repeat the above measurements
as follows:
5. Enter the CCTM command 334 0 to switch off the synthesizer, and
measure the voltage at the via between R104 (see Figure 11.6) and
the digital board.
6. Enter the CCTM command 334 1 to switch on the synthesizer, and
measure the voltage at the via between R104 (see Figure 11.6) and
the digital board.
7. If the voltages measured in Step 5 and Step 6 are still not correct, the
digital board is faulty; replace the main-board assembly and go to
“Final Tasks” on page 123. If the voltages are correct, go to Step 8.
8. There is a fault between the digital board and IC503. Locate the fault.
Check and resolder R104 in position (see Figure 11.6), and check
for continuity between pin 10 of IC503 (see Figure 11.2) and the
digital board via R104.
9. If there is a fault, 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.
pin 10 of IC503: 0 V DC (after entry of CCTM 334 0)
pin 10 of IC503: 2.5 ± 0.3 V DC (after entry of CCTM 334 1)
via at R104: 0 V DC (after entry of CCTM 334 0)
via at R104: 3.3 ± 0.3 V DC (after entry of CCTM 334 1)
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