Tait TP9100 - Page 215

TP9100 Service Manual Frequency Synthesizer Fault Finding 215
© Tait Electronics Limited May 2005
Task 41 —
VCXO Tank Circuit
If the CCTM checks indicate that the VCXO tank circuit is faulty, repair
the circuit as follows:
1. If not already done, remove the
VCXO BOT can.
2. Locate and repair the fault in the VCXO tank circuit (Q501, D501,
D502, XL501 and associated components) (see Figure 9.20).
3. Confirm the removal of the fault and go to Step 4. If the repair failed,
replace the main board and go to “Final Tasks” on page 134.
4. Replace all cans.
5. Repeat Ta sk 4 0
to confirm the removal of the fault. If the repair
failed, replace the main board and go to “Final Tasks” on page 134.
Task 42 —
CODEC 2 Circuitry
If the CCTM checks indicate a fault in the CODEC 2 circuitry or with the
digital signals to and from the circuitry, rectify the fault as follows:
1. Most of the CODEC 2 circuitry is situated under the
CDC TOP can.
If not already done, remove the
CDC TOP can.
2. Check the following digital signals at IC205 (see Figure 9.22):
■ pin 10 : DIG CDC2 LRCK
■ pin 12 : DIG CDC2 SCLK
■ pin 8 : CDC2 DIG SDTO
■ pin 9 : DIG CDC2 SDTI
These signals to and from the digital circuitry should all be active:
3. If the digital signals are correct, the CODEC 2 circuitry is suspect; go
to Step 6. If they are not, go to Step 4.
4. If any or all digital signals are missing, check the connections between
IC205 and the digital circuitry (see Figure 9.22).
5. If there are faults such as open circuits in the connections, repair the
circuitry and repeat Ta sk 40
.
If the connections are not faulty, then the digital circuitry is faulty.
Replace the main board and go to “Final Tasks” on page 134.
6. The CODEC 2 circuitry comprises IC205 and associated
components under the
CDC TOP can. Locate the fault.
7. Repair the circuitry. Note that, if the circuitry is functioning properly,
probing the
TP501 test point (see Figure 9.21) during power-up
will show a five-step staircase signal followed by a random nine-step
staircase signal — this is the expected power-up auto-calibration
sequence.
digital signals: 3.3 ± 0.3V