TM8100/TM8200 Service Manual
Frequency Synthesizer Fault Finding
237
© Tait Electronics Limited
June 2006
9.11
VCXO and CODEC Circuitry
Introduction
If the signals at the
TP
501
and
TP
502
test points are correct, two CCTM
checks will reveal any remaining faults. These possible faults concern the
VCXO tank circuit and the CODEC 2 circuitry. There are therefore three
aspects, which are covered in
■
■
: VCXO tank circuit
■
: CODEC 2 circuitry.
Following any repairs of the VCXO or CODEC 2 circuitry,
will
need to be repeated to confirm the removal of the fault.
Task 40 —
CCTM Checks
If the signals at the
TP
501
and
TP
502
test points are correct, or any related
faults were rectified, perform the following CCTM checks:
1.
Enter the CCTM command
393 1 1900
. Measure the voltage level at
the
TP
501
test point
(see
):
2.
Enter the CCTM command
72
and note the lock status.
3.
Enter the CCTM command
393 1 –1900
. Again measure the voltage
level at the
TP
501
test point
:
4.
Enter the CCTM command
72
and note the lock status.
5.
If the above voltage levels are not correct or if the FCL is out of lock
in either or both of the above cases, investigate the VCXO tank
circuit; go to
If the voltage level remains fixed at about 1.5V DC, investigate the
CODEC 2 circuitry; go to
If the voltage levels are all correct (following earlier repairs), the fault
has been removed; go to
Task 41 —
VCXO Tank Circuit
If the CCTM checks indicate that the VCXO tank circuit is faulty, repair
the circuit as follows:
1.
If not already done, remove the
VCXO
BOT
can.
2.
Locate and repair the fault in the VCXO tank circuit (
Q501
,
D501
,
D502
,
XL501
and associated components) (see
3.
Confirm the removal of the fault and go to
. If the repair failed,
replace the board and go to
.
TP501 test point: 1.3
±
0.2 V DC (after CCTM 393 1 1900)
lock status=
xyz
(
x
=RF PLL;
y
=FCL;
z
=LO2) (0=not in lock; 1=in lock)
TP501 test point: 2.1
±
0.2 V DC (after CCTM 393 1 –1900)
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...
