Tait TM8100 mobiles Service Manual page 241

Task 38 —
TP501 Test Point
TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Also, the VCXO input to the mixer (see
noisy and difficult to measure, should be:
VCXO input at R522 (pin 1 of IC501):
VCXO input: sine wave of 20 ± 10 mV
A4 band: VCXO input at R510 (pin 1 of IC506):
VCXO input: sine wave of 20 ± 10 mV
6. Confirm the removal of the fault and go to
failed, replace the board and go to
502 test point is correct, check the signal at the
If the signal at the
TP
test point:
1. With the oscilloscope probe at the
(see Figure 9.18), check the DAC output
triangular wave is present, go to
CODEC Circuitry" on page
2. A fault is causing the loop to oscillate. If not already done, remove the
can.
FCL TOP
3. Check the waveform at the
The waveform should be an amplified and inverted version of the
waveform at the
500 is not marked, but the waveform can be checked at
A4 band:
TP
the via adjacent to C518.
4. If the waveform is correct, go to
the modulator buffer amplifier (IC502 pins 1 to 3, and associated
components) (see
501 test point to ground by resoldering R527 in the
5. Connect the
TP
position shown in
6. 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
7. If the signal is correct, go to
8. The VCXO circuitry is faulty. If not already done, remove the
can.
BOT
9. Locate and repair the fault in the VCXO circuitry (Q501, Q503,
XL501 and associated components) (see
10. Confirm the removal of the fault, and go to
failed, replace the board and go to
pp
pp
"Final Tasks" on page
501 test point
TP
Step 2. Otherwise go to
244.
500 test point (see
TP
501 test point.
TP
Step 5. If it is not, there is a fault in
Figure 9.18). Rectify the fault and return to
Figure 9.18. The VCXO loop voltage is forced high.
Figure
amplitude of 1.1 ± 0.2V
Task 39. If it is not, go to
"Final Tasks" on page
Frequency Synthesizer Fault Finding
Figure 9.18), although
Task 38. If the repair
163.
TP
. If a
CDC VCXO MOD
"VCXO and
Figure 9.18).
Step
9.18). The signal should be:
on 1.4 ± 0.2V DC
pp
Step 8.
Figure 9.19).
Task 39. If the repair
163.
501
1.
VCXO
241