Phase-Locked Loop - Tait TM8100 mobiles Service Manual

9.3

Phase-locked Loop

Introduction
Task 7 —
Supply for
Charge Pump
198 Frequency Synthesizer Fault Finding
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
Task 10: line output.
■
SYN LOCK
The measurement points for diagnosing faults concerning the PLL inputs
and output are summarized in
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).
pin 16 of IC503: 5.0 ± 0.3V DC
2. If the voltage is correct, go to
3. Check the C-multiplier Q512 (see
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
could be found, replace the board and go to
page 163.
line input
Figure 9.6.
Task 8. If it is not, go to
Figure
163. If the repair failed or no fault
© Tait Electronics Limited November 2007
Step 3.
9.2) and check IC503
"Final Tasks" on
TM8100/TM8200 Service Manual