Motorola APX 3000 Detailed Service Manual page 131

Troubleshooting Charts: VCO Failure
VCO Failure – Page 4
Replace suspected
Yes
components.
(UHF2)
At Rx, is L701 high and
Check continuity at
No
L702 low?
L701 and L702.
At Tx, is L701 low and
Fault found?
L702 high?
Yes
No
Replace U702.
Is power at U3001 input
Tx: C3112
Rx: C3102
>-20dBm?
Yes
Check parts around
U3001. If OK,
replace U3001.
3
Is power at
No
C3161
>-20dBm?
Yes
Control voltage
No
at R705
0.3<Vdc<10.6?
No
Take continuity
check of traces to
Yes
U702.
Is Vdc = 4.55V at pin
No
3 of Q3123 during
Rx and at Q3156
during Tx?
Yes
For Tx: Check and visual inspect D3135 -
D3138, C3140, C3141, C3143, C3147,
L3139, L3145.
For Rx: Check and visual inspect D3102 -
D3105, C3107, C3108, C3110, C3113,
L3106, L3112.
Is Vdc at C742 5V,
No
Check 2.775V and
Vdc at C726, C734,
5V supply.
C737 2.775V?
Yes
No Check 2.775V
Is Vdc at Y701
supply.
pin 4 2.775V?
Yes
No
16.8MHz at pin
Replace Y701
3 of Y701 and
and/or C736.
C736?
Yes
Check and visual
No
16.8MHz at
inspect U746 circuitry.
L753?
Fault found?
Yes
No
No
Yes
10.8Vdc at pin2
Replace U702.
of D723?
No
Check D722, D723,
Yes
2.775Vdc at pin
C716, C717, C718,
4 of D722?
C719.
5-41
Replace the
Yes
suspected
components.