Motorola GP series, Detailed Service Manual

Page: 461 / 494

Troubleshooting Flow Chart for VCO 2-5
5.0 Troubleshooting Flow Chart for VCO
Is
the Tx RF
level at C254 about
0dBm
?
Are
the bias
voltages of Q251
as indicated
?
Is the
1.9V present at
R266 as indi-
cated
?
START
Is LO signal
present at the
mixer IC U301?
Check the 4.6V
biasing circuitry
and pin 28 of
U201.
Yes
Is resonator IC
U205 soldered
OK?
Is
TRB pin 19
of U250 low
?
Is
the 1.9V
present at R265
as indicated
?
Is the
steering line
voltage
VCTRL 0V or
13V
?
Is the
LO RF level at
C253 about
0dBm
?
Are
the bias
voltages of Q304
as indicated
?
No
Yes
Yes
Is
the PRESC
RF level at C227
as indicated
?
No
No
No
Troubleshoot the
Synthesizer.
Check Q252 and
Q200.
Yes
No Yes
Is Tx signal
present at the PA
driver IC, U101?
Is resonator
IC U206 sol-
dered OK?
Is
TRB pin 19 of
U250 high
?
Is
the steering
line voltage
VCTRL 0V or
13V
?
No
Yes
Yes
VCO is OK.
Is
the 4.6V
VSF voltage
present at pins
3, 18, & 14 of
U250
?
Is the
4.6V VSF
voltage present at
pins 3, 18, & 14
of U250
?
Is
pin 2 (AUX3)
of U201 high
?
No
Troubleshoot the
Synthesizer.
Check Q252 and
Q200.
Yes
Check the 4.6V
biasing circuitry
and pin 28 of
No
Replace U250.
Yes
Replace U250.
No
Replace U250.
No
Yes
Is
the PRESC
RF level at C227
as indicated
?
No
Replace U250.
Yes
Replace U250.
Tx VCO OK.
No
Yes
Yes
No
Check Q251 and
its bias circuitry.
Check Q304 and
its bias circuitry.
No
Yes
Yes
Yes
Replace U250.
Rx VCO OK.
No
Yes
Resolder or
replace
U206.
Resolder or
replace
U205.
Yes
No
No
No
Yes
Yes
No
No
Is pin 3
(AUX4) of
U250 low?