TM8100/TM8200 Service Manual
Frequency Synthesizer Fault Finding
219
© Tait Electronics Limited
June 2006
Task 28 —
Check VCO
Check that the correct receive and transmit frequencies are synthesized.
The receive frequency is that of the VCO output
SYN
RX
LO
1
at the
RX
port
shown in
. The transmit frequency is that of the output
SYN
TX
LO
at the
TX
port.
1.
Enter the CCTM command
335 1
to set the transmit-receive switch
on (transmit mode).
2.
Using a frequency counter, proceed as follows to observe the transmit
frequency at the
TX
port before and after grounding the junction
between
C541
and
R547
(see
While holding the probe from the counter on the
TX
port, use a pair
of tweezers to momentarily ground the junction. The frequency
should change to:
The loop filter will hold its output steady at 13.3 V. This should result
in a frequency equal to the maximum given in
3.
If the maximum frequency measured in
is correct, go to
. If it is incorrect, go to
, but if no frequency at all is
detected, go to
.
4.
Enter the CCTM command
335 0
to set the transmit-receive switch
off (receive mode).
5.
Proceed as follows to observe the receive frequency at the
RX
port
before and after applying 3 V DC to the junction of
C541
and
R547
;
there is a convenient 3 V level at
R544
(see
While holding the probe on the
RX
port, use the tweezers to
momentarily apply 3 V DC to the junction; do not touch the board
with your hand, and do not allow the tweezers to touch any cans
when you remove them. The frequency should change to:
The loop filter will hold its output steady at about 0V. This should
result in a frequency equal to the minimum given in
6.
If the minimum frequency measured in
is correct, go to
. If no frequency is detected,
go to
TX port: maximum VCO frequency (see
RX port: minimum VCO frequency (see
)
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...
