5.16 Fgu Failure - Motorola APX 7000 Detailed Service Manual

Troubleshooting Charts: FGU Failure

5.16 FGU Failure

VCO TX/RX
unlock
"Sniff "
Frequency near
VCO shield
Frequency
detected?
Yes
Remove
VCO shield.
Check control
Voltage at R764.
<1Vdc
>10Vdc
or drifting?
Yes
Remove
TRIDENT shield.
Check power
on prescalar buffer
output ,C779 using
field probe.
Is power at
No
C779
> -15dBm?
Yes
Check parts
around VCOs and
loop filter. If OK,
replace VCO.
See Note 2
No
2.5V at
logic pins
on U708?
See Note 3
Yes
Replace U708.
Sniff: Using an inductive field probe
as an antenna to measure
frequency. Place the probe
approximately ½ inch away from
components to be sniffed
No
Remove
VCO shield.
around U703.
If OK, replace
Check if VCO
No
Is locked using
spectrum analyzer.
Locked?
Check
VOCON board.
Is power at
Yes
U709 output
> -15dBm?
No
Check parts around
Is power at
Q774. If OK,
No
VCO output
replace Q774.
> -15dBm?
Yes
Yes No
VHF TX?
See Note 3
Replace U709.
No
Remove
4.6V at
TRIDENT shield.
TP853?
Yes
Check parts
2.5V at
No
logic pins
on U703?
U703.
Yes
Replace VCO.
No
VCO
Remove
TRIDENT shield.
Yes
Check parts
around U702.
If OK, replace
U702.
No Check
1.5Vdc at
1.5V DC supply.
L701?
Yes
Check parts
2.5V at
No
around U703.
logic pins
If OK, replace
on U709?
U703.
Yes
No
5V at
C742?
Yes
See Note 1
See Note 2
Note 1:
Pin Freq Band
4 VHF RX
8 VHF TX
10 700 RX / 800 TX
9
700 TX / 800 RX
6 7/800 TX
8 UHF1 RX (380-450)
15 UHF1 /UHF2 RX (450-520)
12
UHF1 TX (380-445)
13 UHF1/UHF2 TX (445-520)
Note 2:
Ref Des
Y704 VHF TX / UHF1 / UHF2 RX
Y705 UHF1 / UHF2 TX
Y706 Y705 700 / 800 RX / TX
Y707 700 800 TX / VHF RX
Note 3:
Pin Pin Freq Band Freq Band
700 / 800 RX
3
6
VHF TX / UHF RX / UHF TX
U709
7 VHF RX / 7/800 TX
6
VHF TX / UHF RX
U708
UHF TX
3
5-45
Check
5V DC supply.
Check parts
around U702.
If OK, replace
U702.
VCO
/ TX