TM8100/TM8200 Service Manual
Frequency Synthesizer Fault Finding
211
© Tait Electronics Limited
June 2006
Task 22 —
Check Receive
Buffer Amplifier
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
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
.
If they are not, the receive buffer amplifier is suspect; go to
7.
Remove the
VCO
TOP
can.
8.
Check the receive VCO circuitry based on
Q504
(see
Conclude with
.
9.
Check the first buffer stage (based on
Q5100
) and the second stage
(based on
IC5100
) (see
).
10.
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
.
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)
Summary of Contents for TM8235
Page 1: ...TM8100 mobiles TM8200 mobiles Service Manual MMA 00005 04 Issue 4 June 2006...
Page 10: ...10 TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 62: ...62 Description TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 148: ...148 Disassembly and Reassembly TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 162: ...162 Servicing Procedures TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 178: ...178 Interface Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 258: ...258 Receiver Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 446: ...446 Spare Parts TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...