Motorola GP68, Service Manual

Page: 58 / 85

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