Tait TP9100 - Page 280

280 CODEC and Audio Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 8 —
Check LPF and
Buffer Amplifier
If there is no test signal at the connector PL1, then either CODEC 1 is
faulty or there is a fault in the LPF or buffer amplifier.
1. Remove the
CDC BOT can.
2. At the test set apply 60%, 1kHz modulation to the RF signal.
Reduce the volume to a minimum.
3. Check the signal at R224 (see Figure 12.5). This should be:
4. If the above signal is correct, go to Step 5. If it is not, CODEC 1
(IC204) is faulty; replace the main board and go to “Final Tasks” on
page 134.
5. Check the voltage at pin 1 of IC201 (see Figure 12.5).
6. If the voltage is correct, go to Step 7. If it is not, check the LPF
circuit based on IC201 (pins 1 to 3) (see Figure 12.5). Repair any
fault and conclude with Step 10.
7. Check the voltage at pin 7 of IC201 (see Figure 12.5).
8. If the voltage is correct, go to Step 9. If it is not, check the buffer
amplifier based on IC201 (pins 5 to 7) (see Figure 12.5). Repair any
fault and conclude with Step 10.
9. Check R207 and R208 (see Figure 12.5). Repair any fault and
conclude with Step 10.
10. Confirm the removal of the fault and go to Step 11. If the repair failed
or the fault could not be found, replace the main board and go to
“Final Tasks” on page 134.
11. If there is also a fault with the transmit modulation, notwithstanding
modulation at the accessory connector, go to “Faulty Modulation
Using Accessory Audio Tap In” on page 287. If there is no other
fault, go to “Final Tasks” on page 134.
R224: 0.7 V
pp
with 1.2V DC offset
pin 1 of IC201: 0.7V
pp
with 1.2V DC offset
pin 7 of IC201: 0.7V
pp
with 1.2V DC offset