Tait TM8100 mobiles, Service Manual

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TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 237
© Tait Electronics Limited November 2007
9.9 VCXO and TCXO Outputs
Task 35 —
VCXO Output
If the 3V power supply is not faulty, check the VCXO output as follows:
1. Use an oscilloscope probe to check the VCXO output at the
following position:
2. If the signal is correct, go to Task 36 . If it is not, go to Step 3 .
3. The VCXO circuitry under the
VCXO BOT
can is faulty. Remove the
VCXO BOT
can.
4. Locate and repair the fault in the VCXO ( Q501 , Q503 , XL501 and
associated components) (see Figure 9.19 ).
5. Confirm the removal of the fault and go to Task 36 . If the repair
failed, replace the board and go to “Final Tasks” on page 163 .
C536 — probe the via next to C536 (see Figure 9.18 ). The signal
should be:
VCXO output at C536: sine wave of 1.1
±
0.2V
pp
on 1.4
±
0.2V DC
A4 band:
IC509, pin 4
— probe the via next to
R5044
(see Figure 9.18 ). The signal should be:
VCXO output at pin 4 of IC509: square wave of 1.5
±
0.2V
pp