Motorola Cm Radio Vhf2 Information Manual

Chapter 3
TROUBLESHOOTING CHARTS
This section contains detailed troubleshooting flowcharts. These charts should be used as a guide in 
determining the problem areas. They are not a substitute for knowledge of circuit operation and 
astute troubleshooting techniques. It is advisable to refer to the related detailed circuit descriptions 
in the theory of operation sections prior to troubleshooting a radio.
Most troubleshooting charts end up by pointing to an IC to replace. It is not always noted, but it is...

3-2TROUBLESHOOTING CHARTS
1.0 Troubleshooting Flow Chart for Receiver RF (Sheet 1 of 2)
Problem in 12 KHz and 
25 KHz channel spacing
9V on
R310 (LNA)
OK?Check
RX_ENNoGo to 
DC Section
Ye s
RX_EN
ON ?NoCheck Q306, Q300 
and U403Ye s
START
LOC_DIST
ON?Check Q304, D305 
and U403
LO
POWER
OK ?
Go to SYN 
Section
Ye s
Ye s No
No
Go
to A
Ye s
3 V
to U301
Okay ?No
Check
LOC_DIST
Go to
DC Section
Ye s
Check D301-304
Replace IF Filters( FL304, FL301)
If problem in 25 KHz spacing
Check
TPI
Check 5V
on R336 
5V...

Troubleshooting Flow Chart for Receiver RF (Sheet 1 of 2) 3-3
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
3V
(IFIC -Vcc)
OK ?
Installation
OK ?
Ye s
Ye s No
No
A From
Check visually
all receiver
components
installation ?
Inject - 40dBm (CW)
to RF connector
Check Power on
C332 
RF
Power
> -28 dBM?Ye s NoCheck Power on
C336 
Go to 
DC Section
Check 
the component
Antenna to Mixer 
circuitry problem
Replace 
Q303, Q301
Check passive
componentsRF
Power
> -28 dBM?Ye s
NoReplace 
Q305, Q300,...

3-4TROUBLESHOOTING CHARTS
2.0 Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3)
START
Ye s
No
Check components between 
Q100 and RF output, 
Antenna Switch D104, 
D103, VR102 and Q106 be-
fore replacing Q100
No or too low power when keyed
Current
increase when 
keyed?
Check power settings, tuning 
& components between U103 
Pin 3 and ASFIC Pin 6 before 
replacing ASFIC
Control 
Voltage at 
TP150
=1.5V?Check PA 
Stages
>1.0A
Voltage U103 
pin 5 = 
4.7V?
U103 Pin 3 
2Vdc
Check 9.3V 
Regulator...

Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 3-5
2.1Troubleshooting Flow Chart for 25W Transmitter (Sheet 2 of 3)
Ye s
5V
2-5V
2-3V
Ye s No
3V 

3-6TROUBLESHOOTING CHARTS
2.2Troubleshooting Flow Chart for 25W Transmitter (Sheet 3 of 3)
No
Ye s
Ye sNo
Check Final PA Stage
PA_Bias 
Voltage at 
R134 
2.1V
RF Voltage 
after C1044 -
>100mV?
Voltage 
across R122 
>50mV?
RF Voltage 
Q105 gate 
>100mV?
RF Voltage 
Q100 gate 
>1.5V?
Check components 
between Q100 & 
antenna connector
Replace Q100
Check FGU 
Check components 
between C1044 & 
C1117
Check components 
between C1117 & 
Q105
Check components 
between Q105 & 
Q100
No
No Ye s Ye s 2-3VSupply...

Troubleshooting Flow Chart for Synthesizer3-7
3.0 Troubleshooting Flow Chart for Synthesizer
+5V at 
U200 Pins
13 & 30? 5V
 at pin 6 of 
D200
Is information
from µP U403
correct?
Is U200 
Pin 47
= 13VDC?
Is U201 Pin 19
4.5 VDC in TX?  
(at VCO section)
Sta rt
Visual 
check of the 
Board OK?Correct
Problem
Check 5V
Regulator 
U503
Is 16.8MHz
Signal at
U200 Pin 19?
Check
Y201 and associated 
parts
Are signals
at Pins 14 &
15 of U200?
Check 
R228
Check R201Is U200 pin 2  
>4.5 VDC in Tx & 

3-8TROUBLESHOOTING CHARTS
4.0 Troubleshooting Flow Chart for VCO
Are Q200
Base at 2.4V 
Collector at 4.5V 
Emitter at 1.7VAre U201 Pins
13 at 4.4V
15 at 1.1V
10 at 4.5V
16 at 1.9V
Low or no RF Signal
at TP1
Visual check
of board
OK?
35mV DC at
U201 Pin 19
NO
YES
at base of Q200
NO
NO
NO
NO YES
YES
YES
YESLow or no RF Signal
at input to PA5V DC at U201
Pin 14 & 18 OK?
4.8V DC at
U201 Pin 19
Is RF available 
at C2060
YES
YESYESYES YES NO
NO
NO
NO
NO
Audio =180mVrms
at “+” side of
D205
2.5VDC
at D205
If...

Troubleshooting Flow Chart for DC Supply (1 of 2) 3-9
5.0 Troubleshooting Flow Chart for DC Supply (1 of 2)
Since the failure of a critical voltage supply might cause the radio to automatically power down, 
supply voltages should first be probed with a multimeter. If all the board voltages are absent, then 
the voltage test point should be retested using a rising-edge-triggered oscilloscope. If the voltage is 
still absent, then another voltage should be tested using the oscilloscope. If that voltage is...

3-10TROUBLESHOOTING CHARTS
5.1 Troubleshooting Flow Chart for DC Supply (2 of 2)
Check VDC on
C5007
V=3.3V
?Check Voltage on 
C5041NoGo to Digital SectionYe s
9v