Service manual

3-40 900 MHz Troubleshooting Charts
5V
at pin 6 of
D201.
Is information
from
µP U409
correct?
Is U201 Pin 28
at 4.6 VDC?
Is U201 Pin 47
AT = 13 VDC
Start
Visual
check of the
Board OK?
Correct
Problem.
Check 5V
Regulator.
+5V at U201
Pin’s
13 & 30?
Is 16.8MHz
Signal at
U201 Pin 19?
Check Y201, C235,
C237, C236, CR203
& R211.
Are the
waveforms
at Pin’s 14
&15 of U201
rectangular?
Check
L200.
Replace U201.
Remove
Shorts.
Is there a short
between Pin 47 and
Pins 14 & 15 of
U201?
Replace or
resolder
defective
components.
Is RF level at
U201 Pin 32
as indicated?
Are C226, R209,
R210, L204, C231,
C801, C802, C803,
C804, C805, C225,
C218, R216, and
R217 OK?
Replace U201.
If L203, C227 & C228
are OK, then see VCO
troubleshooting chart.
Are Waveforms
at Pins 14 & 15
triangular?
Do Pins 7,8 & 9
of U201 toggle
when channel is
changed?
Check programming
lines between U409
and U201 Pins 7,8 & 9.
Replace U201
Check uP U409
Troubleshooting
Chart.
NO
YES
NO
YES
NO
YES
NO
NO
YES
YES
NO
YES
YES
NO
YES
YES
YES
NO
NO
NO
NO
YES
NO
YES
Check D201, D202,
C244, C245, C246 &
C247.
3.3V at U201
pins 5, 20, 34
&36.
Check U248
& L202.
Is
16.8MHz
signal at
U201 pin
23?
Replace
U201.
YES
NO
NO
YES
NO
YES
Troubleshooting Flow Chart for Synthesize
r
Is resonator
FL202
soldered
OK?
Is the Tx RF
level at C254
about 0dBm?
Are the bias
voltages of
Q251 as indi-
cated?
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
Troubleshooting Flow Chart for VCO
Is resonator
FL201 soldered
OK?
Is TRB pin 19
of U250 low?
Is the 1.9V
present at
R265as indi-
cated?
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 indi-
cated?
No
Yes
Yes
Is the PRESC
RF level at
C227 as indi-
cated?
No
No
No
Troubleshoot the
Synthesizer.
Check Q252 and
Q200.
Yes
No
Yes
Is Tx signal
present at the PA
driver IC, U101?
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 U201.
No
Replace U250.
Yes
Replace U250.
No
Replace U250.
No
Yes
Is the PRESC
RF level at
C227 as indi-
cated?
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?