TM9100 Service Manual Frequency Synthesizer Fault Finding 181
© Tait Electronics Limited August 2005
9.3 Phase-locked Loop
Introduction If there is no fault with the power supplies, check the critical output from,
and inputs to, the PLL:
■ Task 7: supply for charge pump
■ Task 8: reference frequency input
■ Task 9: DIG SYN EN line input
■ Task 10: SYN LOCK line output
The measurement points for diagnosing faults concerning the PLL inputs
and output are summarized in Figure 9.5.
Task 7 —
Supply for
Charge Pump
First check the supply for the charge pump of the PLL.
1. Measure the supply for the charge pump at pin 16 of IC503
(see Figure 9.2).
2. If the voltage is correct, go to Task 8
. If it is not, go to Step 3.
3. Check the C-multiplier Q512 (see Figure 9.2) and check IC503
itself; if necessary, replace the transistor or IC.
4. If there is a fault, repair the circuit, confirm the removal of the fault,
and go to “Final Tasks” on page 147. If the repair failed or no fault
could be found, replace the main-board assembly and go to “Final
Tasks” on page 147.
pin 16 of IC503: 5.0 ± 0.3 V DC
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