Troubleshooting Flow Chart For Synthesizer - Motorola HT Series Service Manual

8-34

8.12.8 Troubleshooting Flow Chart for Synthesizer

Check D3701,
D3702, U3701,
C3701 - C3707
YES
NO
5V
Is U3701 Pin 47
at pin 6 of
AT = 13 VDC
D3701
NO
YES
Check
L3701,
R3701
Is U3701 Pin 19
<0.7 VDC in RX &
>4.3 VDC in TX?
YES
I s U 3 7 0 1
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
Correct
Problem
Check Q260,
Q261 & R260
NO
YES
U3701 pin 2 at
>3V in Tx and
<0.7V in Rx
NO
NO
Replace U3701
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 at
NO
U3701
Pin's
13 & 30?
Check 5V
Regulator
NO
Are 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
Maintenance: VHF Troubleshooting Charts
NO
Check U3201,
3.3V at U3701
L3731
pins 5, 20, 34
& 36
YES
16.8MHz
NO
Is 16.8MHz
signal at
Signal at
U3701 pin
U3701 Pin
23?
19?
Check Y3761,
YES
C3761, C3762,
C3763, D3761 &
R3761
NO
Are Waveforms
at Pins 14 & 15
triangular?
YES
Do Pins 7,8 & 9
NO
of U3701 toggle
when channel is
Check programming
lines between U409
and U3701 Pins 7,8 & 9
NO
Is information
from
Check uP U409
Troubleshooting
Chart
Is
Replace
U3701
YES
NO
changed?
YES
µ
P U409
correct?
YES
Replace
U3701