Tait TP9100, Service Manual, Page: 170 / 326

170 Frequency Synthesizer Fault Finding
TP9100 Service Manual
© Tait Electronics Limited May 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 IC503 ; if necessary, replace the IC.
4. If there is a fault, repair the circuit, confirm the removal of the fault,
and go to
“Final Tasks” on page 134 . If the repair failed or no fault
could be found, replace the main board, and go to “Final Tasks” on
page 134 .
Task 8 —
Reference
Frequency
If the supply for the charge pump is correct, check the reference frequency
input from the FCL to the PLL.
1. Measure the reference frequency at pin 8 of IC503 (see Figure 9.3 ).
2. If the signal is correct, go to Task 9 . If it is not, go to Step 3 .
3. Check IC503 (see Figure 9.3 ). Replace IC503 if it is suspect.
4. Determine if the fault has been removed. If it has, go to “Final Tasks”
on page 134 . If it has not, the FCL is suspect; go to “Power Supply
for FCL” on page 205 .
pin 16 of IC503: 5.0
±
0.3V DC
pin 8 of IC503: 13.012
±
0.002 MHz and 1.1
±
0.2V
pp
sine wave