Tait TP9100 - Page 181

TP9100 Service Manual Frequency Synthesizer Fault Finding 181
© Tait Electronics Limited May 2005
Task 15 —
Check
DIG SYN FAST
Line
If the loop filter is suspect but the reference and feedback voltages are
correct, check the
DIG SYN FAST line, which is the input to the inverter Q505.
1. Enter the CCTM command 389 1 to set the synthesizer mode to fast.
2. Measure the voltage at the collector of Q505 (see Figure 9.9).
The result should be:
3. Enter the CCTM command 389 0 to set the mode to slow.
4. Measure the voltage at the collector of Q505 (see Figure 9.9).
The result should be:
5. If the voltages measured in Step 2 and Step 4 are correct, go to
Task 1 6
. If they are not, go to Step 6.
6. Remove R717 (see Figure 9.6).
7. Enter the CCTM command 389 1 to set the mode to fast.
8. Measure the voltage at the via between R717 (see Figure 9.6) and
the digital circuitry. The result should be:
9. Enter the CCTM command 389 0 to set the mode to slow.
10. Measure the voltage at the via between R717 (see Figure 9.6) and
the digital circuitry. The result should be:
11. If the voltages measured in Step 8 and Step 10 are correct, go to
Step 12. If they are not, the digital circuitry is faulty; replace the main
board and go to “Final Tasks” on page 134.
12. Check and resolder R717 in position (see Figure 9.6), and check for
continuity between the collector of Q505 (see Figure 9.9) and the
digital circuitry via R717.
13. If a fault is found, repair the circuit, and confirm that the voltages are
now correct. If they are, go to “Final Tasks” on page 134. If they are
not, or if no fault could be found, replace the main board, and go to
“Final Tasks” on page 134.
Q505 collector: 14.2 ± 0.3V DC (after entry of CCTM 389 1)
Q505 collector: 0V DC (after entry of CCTM 389 0)
via at R105: 0V DC (after entry of CCTM 389 1)
via at R105: 3.3 ± 0.3V DC (after entry of CCTM 389 0)