Motorola GP1280 Series Service Information - Page 26
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Also for Motorola GP1280 Series: Basic Service Manual (46 pages), Service Information (32 pages), Service Information (30 pages)
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3-4
4.0
Troubleshooting Flow Chart for Synthesizer
Check D3701,
Correct
D3702, U3701,
Problem
C3701 - C3707
YES
5V
NO
Is U3701
at pin 6 of
Pin47 AT = 13
D3701
NO
Check
L3701,
R3701
Is
U3701
Pin 19<0.7 VDC
in RX & >4.3 VDC
in TX?
YES
Is
U3701 Pin
18 AT 4.54
VDC?
YES
Is RF level at
U3701 Pin 32
>-30 dBm?
YES
Are
C3721,
C3722,C3723,
R3721, R3722,
R3723
OK?
YES
Replace
U3701
NO
VDC
YES
Check Q260,
Q261 & R260
NO
U3701
YES
pin 2 at >3V
in Tx and
<0.7V in
Rx
NO
NO
Replace
If R3727, C3726 & C3727
NO
are OK, then see VCO
troubleshooting chart
Replace or
NO
resolder
necessary
components
Start
Visual
check of the
Board
OK?
YES
YES
+5V
NO
at U3701
Pin's
13 & 30?
Check 5V
Regulator
Are
NO
signals at
Pin's 14 &15
of U3701
?
YES
Is
there a short
NO
between Pin 47 and
Pins 14 & 15 of
U3701?
YES
Remove
Shorts
TROUBLESHOOTING CHARTS
3.3V
at U3701
NO
Check
pins 5, 20,
U3201,
34 & 36
L3731
YES
Is
16.8MHz
16.8MHz
NO
signal at
Signal at
U3701 pin
U3701 Pin
19?
YES
Check Y3761,
C3761, C3762,
C3763, D3761 &
R3761
Are
Waveforms
NO
at Pins 14 & 15
triangular?
YES
Pins 7,8 & 9
NO
of U3701 toggle
when channel
is changed
Check prgramming
lines between U409
and U3701
Pins 7,8 & 9
NO
information
from mP U409
Check uP U409
Troubleshooting
Chart
Replace
U3701
Is
YES
Replace
U3701
23?
NO
Do
?
YES
Is
correct
?
YES