TM8100/TM8200 Service Manual
Frequency Synthesizer Fault Finding
217
© Tait Electronics Limited
November 2007
Task 22 —
Check Receive
Buffer Amplifier
(not for the
K5 band)
If no receive frequency is detected but the switching network is not faulty,
check the receive buffer amplifier. If the amplifier is not faulty, there might
be a fault in the receive VCO that was not detected earlier.
1.
Remove the
VCO
BOT
can.
2.
Check the receive buffer amplifier in receive mode: Enter the CCTM
command
335 0
to set the transmit-receive switch off.
3.
Measure the voltages at the base of
Q5100
and at pin 4 of
IC5100
(see
Figure 9.12
).
4.
Then check the receive buffer amplifier in transmit mode: Enter the
CCTM command
335 1
to set the transmit-receive switch on.
5.
Again measure the voltages of
Q5100
and
IC5100
.
6.
If the voltages are correct, the receive VCO is suspect; go to
Step 7
.
If they are not, the receive buffer amplifier is suspect; go to
Step 9
.
7.
Remove the
VCO
TOP
can.
8.
Check the receive VCO circuitry based on
Q504
(see
Figure 9.11
).
Conclude with
Step 10
.
9.
Check the first buffer stage (based on
Q5100
) and the second stage
(based on
IC5100
) (see
Figure 9.12
).
10.
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 163
. If they are
not, or if no fault could be found, replace the board and go to
“Final
Tasks” on page 163
.
base of Q5100: 0.7
±
0.1V DC (receive mode)
pin 4 of IC5100: 2.0
±
0.5V DC (receive mode)
base of Q5100: 0V DC (transmit mode)
pin 4 of IC5100: 0V DC (transmit mode)
Содержание TM8100 mobiles
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