TM8100/TM8200 Service Manual
Frequency Synthesizer Fault Finding
233
© Tait Electronics Limited
June 2006
9.10
Signals at TP501 and TP502
Introduction
If the VCXO and TCXO outputs are correct, the next stage is to check the
signals at the
TP
501
and
TP
502
test points. The procedure is divided into
three tasks:
■
: check signal at
TP
502
■
: check signal at
TP
501
and ground
TP
501
if loop is oscillating
■
: check signal at
TP
502
with
TP
501
grounded.
These checks will reveal any faults in the mixer and LPF circuitry, and any
additional fault in the VCXO circuitry.
Task 37 —
TP502 Test Point
Check the signal at the
TP
502
test point to determine if there is a fault in the
mixer or LPF (low-pass filter) 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 or LPF circuitry under the
FCL
TOP
can is faulty. Remove
the
FCL
TOP
can.
4.
Locate the fault in the mixer (
IC501
and associated components) or
LPF circuitry (
IC502
pins 5 to 7, and associated components)
(see
A4 band:
Check the mixer (
IC501
,
IC506
and associated
components) or LPF circuitry (
IC502
pins 5 to 7, and associated
components) (see
L501
and associated
components and buffer
Q504
,
IC509
and associated components.
5.
Repair the circuitry. Note that the TCXO input to the mixer
(see
) should be:
TP502 test point: sine wave of 1.1
±
0.2 V
pp
on 1.5
±
0.1 V DC
A4 band
: The signal should be:
TP502 test point: triangular wave 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
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...
