Tait TM8100 mobiles, Service Manual

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198 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
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 9.6 .
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 163 . If the repair failed or no fault
could be found, replace the board and go to “Final Tasks” on
page 163 .
pin 16 of IC503: 5.0
±
0.3V DC