Motorola Uhf Manual

UHF (403-470MHz) Transmitter Power Amplifier (PA) 40W 2-11
5.8 Power Control
The transmitter uses the Power Control IC (PCIC, U4501) to control the power output of the radio. A 
portion of the forward RF power from the transmitter is sampled by the bi-directional coupler and 
rectified, to provide a DC voltage to the RFIN port of the PCIC (pin 1) which is proportional to the 
sampled RF power. 
The PCIC has internal digital to analog converters (DACs) which provide the reference voltage of the 
control...

2-12THEORY OF OPERATION 

Chapter 3
TROUBLESHOOTING CHARTS
1.0 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)
Bad SINAD
Bad 20dB Quieting
No Recovered AudioSTART
Audio at 
pin 8 of 
U3101 ?Check Controller
(in the case of no audio)
OR ELSE go to “B” Ye s
No
Spray or inject 44.85MHz 
into XTAL Filter FL3101
Audio heard ?BYe s
No
Check 2nd LO 
(44.395MHz) at C3135 
LO present ?BYe s
 Check voltages on 
U3101Biasing OK ?
No
No
A
Ye s
Check Q3102  bias 
for faults
Replace Q3102
Go to B
Ye s
No
Check circuitry 
around U3101....

3-2TROUBLESHOOTING CHARTS
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
IF Signal at 
C3101?
No
RF 
Signal at 
T4051?
RF
Signal at 
C4015?
No
No
RF
Signal at 
C4025?
No or 
Check harmonic filter
L4491-L4493, C4492, J4401
and ant.switch
D4471, D4472, L4472.
Check filter between 
C4025 & C4009. 
Check tuning voltage 
at R4060.
Inject RF into J4401
Is
tuning voltage
OK?
No
Ye s
Check RF amp (Q4003) 
Stage.
Check filter between 
C4015 & T4051.
Ye s
Check T4051, T4052, 
D4051, R4052, L4008.
Ye s
1st...

Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 3-3
2.0 Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3)
Current 
increase 
when keyed?
NO YES
START
Check if Pressure Pad closes S5440
Check Components between 
Q4441 and RF Output, 
Antenna Switch 
D4471,D4472,Q4472, >500mA & 4A
1V
Short TP4403 to 
Ground
NO
YES
Voltage at 
TP4402 
rises?Check PA StagesNO
YES
PCIC U4501 
Pin 14 9.3V 
DC?Check 9.3 V Regulator 
U0641
NO
YESPCIC U4501 
Pin 16 >4V 
DCReplace PCIC U4501
NO
YESTP4404...

3-4TROUBLESHOOTING CHARTS
2.1Troubleshooting Flow Chart for 25W Transmitter (Sheet 2 of 3)
Check PA Stages
No or too low Power when keyed
Measure DC Voltage at Pin 2 & 3 of U4401>6 YESDC Voltage 
at U4501 
Pin 23 =0?
2-6DC Voltage 
at U4402-1 
Pin 1?
YESPin 2
Voltage 0.62 
* Voltage at 
Pin 1?
If U4201 Pin 2 is high,  
replace PCIC
NOReplace U4401
YES NODC 
Voltage at 
U4402-1 Pin 
3 = 8.8V?
Check S4440, 
R4442 and R4443
YESPin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
NOReplace U4401
6V
Check Components...

Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 3-5
2.2Troubleshooting Flow Chart for 25W Transmitter (Sheet 3 of 3)
Check Final PA Stage
NO 0V
1-4VBias 2 DC 
Voltage at 
TP4406?
YESRF Voltage 
at TP4401 
>100mV?
YESRF Voltage 
U4401 Pin 6 
>3V?
Supply
Replace Q4441
Check FGU (U4301)
NOCheck Components 
between 
TP4401  &C4417
NO YESASFIC  
U0221 Pin 6 
1-4V DC?
Check Bias Tuning 
before replacing ASFIC 
U0221
Check Components 
between ASFIC and 
Q4441 before 
replacing Q4441
YESRF Voltage...

3-6TROUBLESHOOTING CHARTS
3.0 Troubleshooting Flow Chart for UHF 40W Transmitter 
No
Is Q4441 OK ?
Ye s
Is drive from VCO
        >+4dBm? NoIs voltage drop across
     R4497 >4.5V ?No
Check Q4431 gate(open)
and drain resistances
            (11kohm)NoCheck Q4421 gate(open)
and drain resistances
             (11kohm)No
        Check
PCIC_MOSBIAS_1
No
No
Change
Q4473 
              START
        No power
  
  Is Vctrl
there? Is Q4473
   OK?
Check voltage
on Pin 5 U4501
Check R4422-5
and go back to top...

Troubleshooting Flow Chart for Synthesizer3-7
4.0 Troubleshooting Flow Chart for Synthesizer
5V
 at pin 6 of 
D4201
Is
information
from
 mP U0101
correct
?
Is
U4201 Pin 47
at = 13VDC
?
Is
U4301 Pin 19
4.5 VDC in TX?  
(at VCO section)
?
Start
Visual 
check of the 
Board
OK?Correct
Problem
Check 5V
Regulator
U4211
+5V
at U4201
Pin’s
13 & 30
?
Is
16.8MHz
Signal at U4201 
Pin 19
?
Check
Y4261 / Y4262 and 
associated Parts
Are
signals
at Pin’s 14 &15 
of U4201
?
Check 
R4201Check C4381
Is
U4201
Pin 2  >4.5...

3-8TROUBLESHOOTING CHARTS
5.0 Troubleshooting Flow Chart for VCO
Are Q4332
Base at 0.7V 
Collector at 4.5V 
Emitter at 110mV
Are Q4301
Base at 2.4V 
Collector at 4.5V 
Emitter at 1.7VAre U4301 Pins
13 at 4.4V
15 at 1.1V
10 at 4.5V
16 at 1.9V
Low or no RF Signal
at TP4003
Visual check
of board
OK?
35mV DC at
U4301 Pin 19
NO
YES
Replace Q4301
at base of Q4332
NO
NO
NO
NO YES
YES
YESYESLow or no RF Signal
at input to PA
4.8V DC at
U4301 Pin 19
Is RF available 
at C4402
YES
YESYES YES NO
NO
NO
NO
NO
Audio...