226
Frequency Synthesizer Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
Task 33 —
Check Buffer
Amplifier
If no VCO frequency is detected but the switching network is not faulty,
check the buffer amplifier. If the amplifier is not faulty, there might be a fault
in the VCO that was not detected earlier.
1.
Enter the CCTM command
335 0
to set the transmit-receive switch
off.
2.
Measure the voltage at pin 3 of
D5004
(see
). (Some RF
noise might be observed.)
3.
Measure the voltage at pin 1 of
Q5001
(see
4.
If the voltages measured in
and
are not correct, go to
. If they are, check the VCO circuitry based on
Q5000
(see
). Conclude with
.
5.
The buffer amplifier is suspect. Check the buffer circuitry (based on
Q5001
) (see
6.
If a fault is found, repair the circuit, and confirm that the voltages are
now correct. If they are, go to
. If they are
not, or if no fault could be found, replace the board and go to
.
pin 3 of D5004: 4.2
±
0.2 V DC
pin 1 of Q5001: 0.7
±
0.2 V DC
Содержание TM8235
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