5.11 Fgu Failure - Motorola APX 3000 Detailed Service Manual

Troubleshooting Charts: FGU Failure

5.11 FGU Failure

FGU Failure
TX Injection
Rx LO low Power?
No
Yes
Correct Tx/Rx
No fault found
frequency?
No
VCO Failure
No
Remove VCO
shield (SH15)
Yes
1.5Vdc at
Tx?
L759?
< 0.5Vdc at
pin 3 of Q767
No
No
Is power at
C817 >
- 20dBm
No
Yes 2.5Vdc at
Check power at input of
U738 logic pin?
U738 pin 1
Yes 2.5Vdc at
Is Power
U738 logic pin?
> -20 dBm?
Yes
No
Check parts around U738.
If OK, replace U738.
No
1.5Vdc at L739
Check 1.5Vdc supply.
Yes
Check parts around
Yes
< 0.5 Vdc at
Q745. If OK, replace
pin 3 of Q745
Q745
No
Yes
Check parts around
Is power at
Q756. If OK, replace
C740 >
Q756.
-20dBm
No
Check 1.5Vdc supply
Yes
Yes
< 1.5Vdc at
pin 2 of Q785
Yes
Check logic in PA Section
Yes
Check parts around Q774.
If OK, replace Q774.
No
Remove FGU shield (SH6)
No
No
< 0.5Vdc at Check parts around Q767. If OK,
pin 6 of Q785
No
Check parts around Q785. If
OK, replace Q785.
Replace U702
5-37
replace Q767.