Check Receive Buffer Amplifier - Tait TM9100 Service Manual

If no receive frequency is detected but the switching network is not faulty,
Task 22 —
Check Receive
check the receive buffer amplifier. If the amplifier is not faulty, there might
Buffer Amplifier
be a fault in the receive VCO that was not detected earlier.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
200 Frequency Synthesizer Fault Finding
Remove the can.
VCO BOT
Check the receive buffer amplifier in receive mode: Enter the CCTM
command 335 0 to set the transmit-receive switch off.
Measure the voltages at the base of Q5100 and at pin 4 of IC5100
(see Figure 9.10).
base of Q5100: 0.7 ± 0.1V DC (receive mode)
pin 4 of IC5100: 2.0 ± 0.5V DC (receive mode)
Then check the receive buffer amplifier in transmit mode: Enter the
CCTM command 335 1 to set the transmit-receive switch on.
Again measure the voltages of Q5100 and IC5100.
base of Q5100: 0V DC (transmit mode)
pin 4 of IC5100: 0V DC (transmit mode)
If the voltages are correct, the receive VCO is suspect; go to
If they are not, the receive buffer amplifier is suspect; go to
Remove the can.
VCO TOP
Check the receive VCO circuitry based on Q504 (see
Conclude with Step 10.
Check the first buffer stage (based on Q5100) and the second stage
(based on IC5100) (see Figure
If a fault is found, repair the circuit, and confirm that the voltages are
now correct. If they are, go to
not, or if no fault could be found, replace the main-board assembly
and go to "Final Tasks" on page
9.10).
"Final Tasks" on page 147. If they are
147.
TM9100 Service Manual
© Tait Electronics Limited August 2005
Step 7.
Step 9.
Figure 9.9).