Troubleshooting Flow Chart For Vco - Motorola HT Series Service Manual

Maintenance: 800 MHz Troubleshooting Charts

8.14.6 Troubleshooting Flow Chart for VCO

Yes
VCO is OK.
No
Check the 4.6V
biasing circuitry
and pin 28 of U201.
Troubleshoot the
Synthesizer.
No
No
Is pin 2 (AUX3)
of U201 high?
Yes
Check Q252 and
Q200.
Replace U250.
No
Is the PRESC
RF level at
C227 as indi-
cated?
Yes
Replace U250.
Yes
Tx VCO OK.
Is Tx signal Yes
present at the PA
driver IC, U101?
No
No
Is resonator
Resolder or
IC U206 sol-
replace U206.
dered OK?
Yes
Is the 4.6V
VSF voltage
present at pins
3, 18, & 14 of
U250?
Yes
Is TRB pin 19
of U250 high?
Yes
No
Is the 1.9V
present at
Replace U250.
R266 as indi-
cated?
Yes
Yes Is the steering
line voltage
VCTRL 0V or
13V?
No
No
Is the Tx RF
level at C254
about 0dBm?
Yes
No
Are the bias
Check Q251 and its
voltages of
bias circuitry.
Q251 as indi-
cated?
START
No
Is LO signal
present at the
mixer IC U301?
Resolder or
replace U205.
Replace U250.
No
Is resonator IC
U205 soldered
OK?
Yes
No
Is the 4.6V
VSF voltage
present at pins
3, 18, & 14 of
U250?
Yes
Is TRB pin 19
of U250 low?
No
Yes
No Is the 1.9V
present at
R265 as indi-
cated?
Yes
Yes
Is the steering
line voltage
VCTRL 0V or
13V?
No
No
Is the LO RF
level at C253
about 0dBm?
Yes
Yes
Are the bias
voltages of
Q304 as indi-
cated?
No
Check Q304 and its
bias circuitry.
8-47
Check the 4.6V
biasing circuitry
and pin 28 of U201.
Troubleshoot the
Synthesizer.
No
Is pin 3 (AUX4)
of U250 low?
Yes
Check Q252 and
Q200.
Replace U250.
No
Is the PRESC
RF level at
C227 as indi-
cated?
Yes
Replace U250.
Rx VCO OK.