Motorola APX 1000 Detailed Service Manual page 147

Troubleshooting Charts: VCO Failure
VCO Failure – Page 4 (UHF2)
Check continuity at
Yes
Replace suspected
L701 and L702.
components.
Fault found?
No
Replace U702.
At Rx, is L701 high and
No No
L702 low?
At Tx, is L701 low and
L702 high?
Yes
No
Is power at U3001 input
Tx: C3112
Rx: C3102
>-20dBm?
Yes
Check parts around
U3001. If OK,
replace U3001.
For Tx: Check and visual inspect D3135-
D3138, C3103, C3140, C3141, C3143,
For Rx: Check and visual inspect D3102-
D3105, C3101, C3107, C3108, C3110,
3
Is power at
C3161
>-20dBm?
Yes
Control voltage
No
at R705
0.3<Vdc<10.6?
Yes
Is Vdc = 4.55V at pin
Take continuity
No
3 of Q3123 during
check of traces to
Rx and at Q3156
U702.
during Tx?
Yes
C3147, L3139, L3145.
C3113, L3106, L3112.
No
Is Vdc at C742 5V,
No Check 2.775V and
Vdc at C726, C734,
5V supply.
C737 2.775V?
Yes
No
Is Vdc at Y701 Check 2.775V
pin 4 2.775V? supply.
Yes
16.8MHz at pin
No
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
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.
5-49
Replace the
Yes
suspected
components.