5.20 Fgu Power Failure - Motorola APX 5000 Service Manual

Troubleshooting Charts: FGU Power Failure

5.20 FGU Power Failure

VCO TX/RX
Low Power
Remove
TRIDENT shield.
No
TX?
Yes
No
1.5Vdc at
L821?
Yes
< 0.5Vdc at
< 1.5Vdc on
Yes
Pin 3 of
Q703?
No
Check logic
Is power
Yes
in PA section.
at C830
> -20dBm?
Check parts
around Q842. If
No
OK, replace Q842.
Check parts
2.5Vdc on
No
around U703. If
U710 logic pin?
OK, replace U703.
See Note 1
Yes
Yes
VHF TX?
> -20dBm?
No
Is power
Yes
at C830
> -20dBm?
> -20dBm?
No
Check parts
around U702. If
OK, replace U702.
Note 1:
U710 Pin Pin
3 700 / 800 / VHF RX / UHF1 RX/ UHF2 RX
6
700 / 800 TX / 7/800 TX / UHF1 TX/ UHF2 TX
7 VHF TX
Remove
at input of U710
VCO shield.
Check 1.5Vdc
supply.
< 0.5Vdc on
No
Pin 2 of
Pin 6 of
Q714?
Q714?
Yes No
Check parts
around Q714. If
OK, replace Q714.
Is power
Check parts
Yes
at C830
around Q842. If
OK, replace Q842.
No
Is power
No
at C799
Yes
Freq Band
Check power
Is power
> -20dBm?
(pin 1).
1.5Vdc at
Check parts
Yes
around Q703. If
OK, replace Q703.
< 0.5Vdc at
Is power
> -20dBm?
2.5Vdc on
U709 logic pin?
See Note 2
Is power
output of VCO
> -20dBm?
See Note 3
Check parts
around VCO. If
OK, replace VCO.
See Note 3
Note 2:
U709 Pin Freq Band
3 VHF TX / UHF1 RX/ UHF2 RX
6
700 RX/TX / 800 RX/TX / UHF1 TX/ UHF2 TX
7
VHF RX / 7800 TX
2.5Vdc on
Yes
U710 logic pin?
See Note 1
No
No
Check parts
around U703. If
OK, replace U703.
No
L806?
Check 1.5Vdc
Yes
supply.
Check parts
Yes
around Q712. If
Pin 3 of
OK, replace Q712.
Q712?
No
Check parts
Yes
at C810
around Q713. If
OK, replace Q713.
No
Check parts
No
around U703. If
OK, replace U703.
Yes
Check parts
Yes
around U709. If
OK, replace U709.
No
Note 3:
Ref Des
Y704 VHF TX / UHF1 RX/ UHF2 RX
Y705 UHF1 TX/ UHF2 TX
Y706 700 RX/TX 800 RX/TX
Y707 7/800 TX / VHF RX
5-47
Check parts
Yes
around U710. If
OK, replace U710.
VCO