5.17 Fgu Power Failure - Motorola APX 7000 Detailed Service Manual

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5.17 FGU Power Failure

VCO TX/RX
Low Power
Remove
TRIDENT shield.
No
TX?
Yes
No
1.5Vdc at
Check 1.5Vdc
L821?
Yes
< 0.5Vdc at
< 1.5Vdc on
Yes
Pin 3 of
Q703?
No
Check logic
Is power
Yes
in PA section.
at C830
> -15dBm?
Check parts
around Q842. If
No
OK, replace Q842.
Check parts
2.5Vdc on
No
around U703. If
U711 logic pin?
OK, replace U703.
See Note 4
Yes
Yes
at pin 8 U711
VHF TX?
> -20dBm?
No
Is power
Yes
at pin 4 U711
> -20dBm?
> -20dBm?
No
Check parts
around U702. If
OK, replace U702.
Note 1:
U710 Pin Pin Freq Band Freq Band
700 / 800 / VHF RX / UHF RX
3
6 700 / 800 TX / 7/800 TX / UHF TX
7 VHF TX
Check power
Remove
at input of U710
VCO shield.
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
around U711. If
OK, replace U711.
No
Is power
No
at C799
Yes
Note 2:
U709 Pin Freq Band Freq Band
700 / 800 RX / TX
3
6 VHF TX / UHF RX / UHF TX
7 VHF RX / 7/800 TX
Is power
> -20dBm?
(pin 1).
1.5Vdc at
L806?
Check parts
Yes
around Q703. If
OK, replace Q703.
< 0.5Vdc at
Pin 3 of
Q712?
Is power
at C810
> -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 3:
Ref Des
Y704
Y705
Y706
Y707
Troubleshooting Charts: FGU Power Failure
Yes 2.5Vdc on
U710 logic pin?
See Note 1
No
No
Check parts
around U703. If
OK, replace U703.
No
Check 1.5Vdc
Yes
supply.
Check parts
Yes
around Q712. If
OK, replace Q712.
No
Check parts
Yes
around Q713. If
OK, replace Q713.
No
Check parts
No
around U703. If
OK, replace U703.
Yes
Yes
No
VHF TX?
No
Yes
Yes
2.5Vdc on
pin 6 U708?
No
Check parts
around U702. If
OK, replace U702.
Note 4:
VCO U711 Pin
700 / 800 TX / 7/800 TX / UHF TX
VHF TX / UHF1 / UHF2 RX 6
7 VHF TX
UHF1 / UHF2 TX
700 / 800 RX / TX
7/800 TX / VHF RX
Check parts
Yes
around U710. If
OK, replace U710.
Check parts
around U709. If
OK, replace U709.
Check parts
around U708. If
OK, replace U708.
Freq Band Freq Band