Signals At Tp501 And Tp502; Tp502 Test Point - Tait TM9100 Service Manual

9.10

Signals at TP501 and TP502

If the VCXO and TCXO outputs are correct, the next stage is to check the
Introduction
signals at the
three tasks:
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
Task 37 —

TP502 Test Point

mixer or LPF (low-pass filter) circuitry:
1.
2.
3.
4.
5.
6.
TM9100 Service Manual
© Tait Electronics Limited August 2005
501 and 502 test points. The procedure is divided into
TP TP
Task 37: check signal at
Task 38: check signal at
Task 39: check signal at
502 test point to determine if there is a fault in the
TP
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
If the signal is correct, go to
The mixer or LPF circuitry under the
the can.
FCL TOP
Locate the fault in the mixer (IC501 and associated components) or
LPF circuitry (IC502 pins 5 to 7, and associated components)
(see Figure 9.16).
Repair the circuitry. Note that the TCXO input to the mixer at
R521 (pin 4 of IC501) (see
TCXO input at R521: square wave with frequency of 13000000 Hz
and amplitude of 3.0 ± 0.2 V
Also, the VCXO input to the mixer at R522 (pin 1 of IC501)
(see Figure 9.16), although noisy and difficult to measure, should be:
VCXO input at R522: sine wave of 20 ± 10 mV
Confirm the removal of the fault and go to
failed, replace the main-board assembly and go to
page 147.
502
TP
501 and ground 501 if loop is oscillating
TP TP
502 with 501 grounded
TP TP
Figure 9.16). The signal is
on 1.5 ± 0.1 V DC
pp
Task 38. If it is not, go to
FCL TOP
Figure 9.16) should be:
pp
Task
Frequency Synthesizer Fault Finding
and
SYN CDC FCL
Step 3.
can is faulty. Remove
pp
38. If the repair
"Final Tasks" on
221