Motorola HT Series Detailed Service Manual page 150

8-60
8.17.9 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
Yes
Is the PRESC
RF level at
C227 as
indicated?
Yes
No
Replace U250.
Yes
Tx VCO OK.
Yes
Is Tx signal
present at the PA
driver IC, U101?
No
No
Is resonator
Resolder or
FL202
replace U206.
soldered
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
indicated?
Yes
Is the steering
line voltage
VCTRL 0V or
13V?
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
indicated?
Maintenance: 900 MHz Troubleshooting Charts
START
No
Is LO signal
present at the
mixer IC U301?
Resolder or
replace U205.
Replace U250.
No
Is resonator
FL201 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
R265as
indicated?
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
indicated?
No
Check Q304 and its
bias circuitry.
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
indicated?
Yes
Replace U250.
Rx VCO OK.