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 Tas k 3 6
. 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
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