TM8100/TM8200 Service Manual
Frequency Synthesizer Fault Finding
235
© Tait Electronics Limited
June 2006
Task 39 —
TP502 Test Point
(TP501 Grounded)
If the loop was oscillating,
will have revealed any fault in the
VCXO circuitry. If there was no fault, or if the circuit was repaired, a check
at the
TP
502
test point is now required. This will show if there are any
additional faults in the mixer or LPF circuitry.
1.
Use the oscilloscope probe to check the difference frequency at the
TP
502
test point
(see
). The signal is
SYN CDC FCL
and
should be:
2.
If the signal is correct, go to
. If it is not, go to
3.
The mixer circuitry (
IC501
and associated components) or the LPF
circuitry (
IC502
pins 5 to 7, and associated components) under the
FCL
TOP
can is faulty (see
). Locate the fault.
4.
Repair the circuitry. Note that the TCXO input to the mixer
(see
) should be:
Also, the VCXO input to the mixer (see
), although
noisy and difficult to measure, should be:
5.
Confirm the removal of the fault, and go to
. If the repair
failed, resolder
R527
in its original position as shown in
replace the board and go to
.
TP502 test point: sine wave with frequency of at least 15kHz and
amplitude of 1.1
±
0.2 V
pp
on 1.5
±
0.1 V DC
A4 band
: the frequency should be:
TP502 test point: triangular wave with frequency of at least 15kHz and
amplitude of 1.5
±
0.2 V
pp
on 1.5
±
0.1 V DC
TCXO input at
R521
(pin 4 of
IC501
):
TCXO input: square wave with frequency of 13 MHz
and amplitude of 3.0 ± 0.2 V
pp
A4 band
: TCXO input at
R520
(pin 4 of
IC506
):
TCXO input: square wave with frequency of 10.4MHz
and amplitude of 3.0 ± 0.2 V
pp
VCXO input at
R522
(pin 1 of
IC501
):
VCXO input: sine wave of 20
±
10 mV
pp
A4 band
: VCXO input at
R510
(pin 1 of
IC506
):
VCXO input: sine wave of 20
±
10 mV
pp
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...
