Tait TM8100 mobiles, Service Manual

Page: 202 / 620

202 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Task 10 —
SYN LOCK
Line
If all the critical inputs to the PLL are correct, check the
SYN LOCK
line
output.
1. Enter the CCTM command
72
to determine the lock status in receive
mode. Note the status.
2. Check the
SYN LOCK
line by measuring the voltage at pin 14 of IC503
(see Figure 9.2 ). The voltage should depend on the lock status as
follows:
3. If the voltage measured in Step 2 is correct, go to “Loop Filter” on
page 204 . If it is not, go to Step 4 .
4. Check for continuity between pin 14 of IC503 and the digital board
via R568 (see Figure 9.2 ) and L102 (see Figure 9.7 ).
5. If there is a fault, go to Step 6 . If there is no fault, the digital board is
faulty; replace the board and go to “Final Tasks” on page 163 .
6. Repair the fault. 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 .
lock status= xyz ( x =RF PLL; y =FCL; z =LO2) (0=not in lock; 1=in lock)
lock status 111 or 110: 3.0
±
0.3V DC at pin 14 of IC503
lock status 011 or 010: 0V DC at pin 14 of IC503