Motorola GP68 Service Manual page 58

Troubleshooting
Troubleshooting Charts
RX VCO
Low or no Power
at Pin 3 of Mixer
NO
VisualCheck
of Board OK?
YES
NO
4.65 VDC at
U251 Pin 13?
YES
NO
0.7 VDC at
U251 Pin 5?
YES
NO
0.01 VDC at
U251 Pin 9?
YES
Are U251 Pin's
2 at 4.2VDC,
7 at 2.1VDC,
10 at 0.8VDC,
11 at 1.6VDC,
12 at 1.2
VDC?
YES
Is 5 VDC at
Collector of
Q251?
Troubleshooting Flow Chart
for VCO
5-6
Correct
Problem
Make sure Synthesizer is
working correctly and
runner between U201 Pin
18 and U251 Pin 13 is OK
Check runner
between U201 Pin 1
and U251 Pin 5
Replace
Replace
L258
L251
If all parts associated
with those Pin's are OK,
then replace U251
NO
NO
Is the
Radio
UHF?
YES
Is +5vRX
at 5V?
YES
NO
YES
Is Q251
Drawing
=4mA
YES
TX VCO
Low or no power
at Input to PA
NO
Visual check
of Board OK?
YES
NO
4.65 VDC at
U251 Pin 13?
NO
4.3 VDC at
U251 Pin 5?
YES
NO
0.01 VDC at
U251 Pin 17?
YES
If all parts from U251 Pin 2 to
Pin 3 of mixer are OK, then
replace U251
NO
Fix the Circuitry
for +5VRX
Replace L269
If all parts around
NO
Q251 are OK,
then replace Q251
6881086C09-O
GP68 Portable Radios Service Manual
Power OK but no
Modulation
NO
=151 mVrms
at "+" Side
of C217?
YES
NO
Replace R252
4.65 VDC
at CR252?
YES
If C256 and R253
are OK, then
replace CR252
Are U251 Pin's
4 at 3.9VDC,
NO
19 at 2.1VDC,
16 at 0.9VDC,
15 at 1.7VDC,
14 at 1.4
VDC?
YES
If all parts from U251
Pin 4 to Input of PA are
OK, then replace U251
Replace
C217
or L255
March, 1997