Tp501 Test Point - Tait TM9100 Service Manual

If the signal at the
Task 38 —

TP501 Test Point

test point:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
222 Frequency Synthesizer Fault Finding
502 test point is correct, check the signal at the
TP
With the oscilloscope probe at the
(see Figure 9.16), check the DAC output
triangular wave is present, go to
CODEC Circuitry" on page
A fault is causing the loop to oscillate. If not already done, remove the
can.
FCL TOP
Check the waveform at the
The waveform should be an amplified and inverted version of the
501 test point.
waveform at the
TP
If the waveform is correct, go to
the modulator buffer amplifier (IC502 pins 1 to 3, and associated
components) (see Figure
Step 1.
501 test point to ground by resoldering R527 in the
Connect the
TP
position shown in Figure
high.
Use the oscilloscope probe to check the VCXO output at C536 —
probe the via next to C536 (see
VCXO output at C536: sine wave with frequency of 13.017 MHz and
amplitude of 1.1 ± 0.2 V
If the signal is correct, go to
The VCXO circuitry is faulty. If not already done, remove the
can.
BOT
Locate and repair the fault in the VCXO circuitry (Q501, Q503,
XL501 and associated components) (see
Confirm the removal of the fault, and go to
failed, replace the main-board assembly and go to
page 147.
501 test point
TP
CDC VCXO MOD
Step 2. Otherwise go to
224.
500 test point (see
Figure
TP
Step 5. If it is not, there is a fault in
9.16). Rectify the fault and return to
9.16. This forces the VCXO loop voltage
Figure 9.16). The signal should be:
on 1.4 ± 0.2 V DC
pp
Task 39. If it is not, go to
Figure 9.17).
Task 39. If the repair
"Final Tasks" on
TM9100 Service Manual
© Tait Electronics Limited August 2005
501
TP
. If a
"VCXO and
9.16).
Step 8.
VCXO