Signals At Tp501 And Tp502 - Tait TM8235 Service Manual

9.10

Signals at TP501 and TP502

Introduction
Task 37 —
TP502 Test Point
TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
If the VCXO and TCXO outputs are correct, the next stage is to check the
501 and
signals at the
TP
three tasks:
Task 37: check signal at
Task 38: check signal at
Task 39: check signal at
These checks will reveal any faults in the mixer and LPF circuitry, and any
additional fault in the VCXO circuitry.
Check the signal at the
mixer or LPF (low-pass filter) circuitry:
1. Use the oscilloscope probe to check the difference frequency at the
502 test point (see
TP
should be:
TP502 test point: sine wave of 1.1 ± 0.2 V
A4 band: The signal should be:
TP502 test point: triangular wave of 1.5 ± 0.2 V
2. If the signal is correct, go to
3. The mixer or LPF circuitry under the
the can.
FCL TOP
4. Locate the fault in the mixer (IC501 and associated components) or
LPF circuitry (IC502 pins 5 to 7, and associated components)
(see Figure 9.17).
A4 band: Check the mixer (IC501, IC506 and associated
components) or LPF circuitry (IC502 pins 5 to 7, and associated
components) (see
components and buffer Q504, IC509 and associated components.
5. Repair the circuitry. Note that the TCXO input to the mixer
(see Figure 9.17) should be:
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
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
502 test points. The procedure is divided into
TP
502
TP
501 and ground
TP
502 with 501 grounded.
TP TP
502 test point to determine if there is a fault in the
TP
Figure 9.17). The signal is
Task 38. If it is not, go to
Figure 9.17). Also check L501 and associated
Frequency Synthesizer Fault Finding
501 if loop is oscillating
TP
SYN CDC FCL
on 1.5 ± 0.1 V DC
pp
on 1.5 ± 0.1 V DC
pp
Step 3.
can is faulty. Remove
FCL TOP
pp
pp
and
233