Tx Or Rx Vco Unlock (Fail 001) (136-174 Mhz)-Part 2 Of 2 - Motorola ASTRO XTL 1500 Detailed Service Manual

Digtal, vhf/uhf range 1/uhf range 2/700–800 mhz
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Troubleshooting Charts: Flowcharts
5.6.10 TX or RX VCO Unlock (Fail 001) (136–174 MHz)—Part 2 of 2
3VDC
A
at pin 5 of
U3750?
Yes
Check 3 Volt
supply path from
Regulator U3750
Unlock
RX or
TX?
RX
Aux 3
or 4 at 3.0VDC
for RX?
Yes
8.2VDC
at TP6761 or
TP6763?
Yes
Check components
around Q3751 or
Q3752, if OK,
replace Q3751 or
Q3752 respectively
Figure 5-12. TX or RX VCO Unlock (Fail 001) (136–174 MHz)—Part 2 of 2
6815854H01-A
Check 5 Volt
No
supply path from
regulator U0505
Refer to Chart to determine
which AUX output determines
active VCO.
TX
No
Check
U3751
Check
No
Q3766 or
Q3764
Aux 1
No
or 2 at 3.0VDC
for TX?
Yes
8.2VDC
No
at TP6772 or
TP6760?
Yes
Check components
around Q3753 or
Q3754, if OK,
replace Q3753 or
Q3754 respectively
5-21
Check
U6751
Check
Q3765 or
Q3763
AEPF-27818-O
June 15, 2005

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