Motorola APX 1000 Detailed Service Manual page 148

5-50
VCO Failure – Page 5 (VHF)
No
Is power at U3238 input
Tx: C3160
Rx: C3159
>-20dBm?
Yes
Check parts around
U3238. If OK,
replace U3238.
4
Is power at
C3240
>-20dBm?
Yes
No Control voltage
at R705
0.3<Vdc<10.6?
Yes
Is Vdc at R3200 high at
No
Rx and low at Tx and
R3202 high at Tx and
low at Rx?
Yes
Is Vdc = 4.55V at pin
3 of Q3227 during
Rx and at Q3267
during Tx?
Yes
For Tx: Check and visual inspect D3246-
D3249, L3250, C3251, C3252, C3254,
C3256, C3258.
For Rx: Check and visual inspect D3206-
D3209, L3210, C3211, C3212, C3214,
. L3216, C3217.
Is Vdc at C742 5V,
No
Vdc at C726, C734,
C737 2.775V?
Yes
Is Vdc at Y701
pin 4 2.775V?
Take continuity
check of traces to
U702.
Yes
16.8MHz at pin
3 of Y701 and
C736?
No
Yes
16.8MHz at
L753?
Yes
No
10.8Vdc at pin2
of D723?
No
2.775Vdc at pin
4 of D722?
Troubleshooting Charts: VCO Failure
No
Check 2.775V and
5V supply.
No Check 2.775V
supply.
No
Replace Y701
and/or C736.
Check and visual
No
inspect U746 circuitry.
Fault found?
No
Yes
Replace U702.
Check D722, D723,
Yes
C716, C717, C718,
C719.
Replace the
Yes
suspected
components.