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 loop. The reference voltage level is programmable through the SPI line of the PCIC. This 
reference voltage is proportional to the desired power setting of the transmitter, and is factory 
programmed at several points across the frequency range of the transmitter to offset frequency 
response variations of the transmitter s power detector circuitry.
The PCIC provides a DC output voltage at pin 4 (INT) which is applied as CNTLVLTG to the power-
adjust input pin of the first transmitter stage U4401. This adjusts the transmitter power output to the 
intended value. Variations in forward transmitter power cause the DC voltage at pin 1 to change, and 
the PCIC adjusts the control voltage above or below its nominal value to raise or lower output power.
Capacitors C4502-4, in conjunction with resistors and integrators within the PCIC, control the 
transmitter power-rise (key-up) and power-decay (de-key) characteristic to minimize splatter into 
adjacent channels.
U4502 is a temperature-sensing device, which monitors the circuit board temperature in the vicinity 
of the transmitter driver and final devices, and provides a dc voltage to the PCIC (TEMP, pin 29) 
proportional to temperature. If the DC voltage produced exceeds the set threshold in the PCIC, the 
transmitter output power will be reduced so as to reduce the transmitter temperature. 
						

							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.
Replace 
U3101 if defectCheck circuitry around Y3101 Re-
place Y3101 if defectVoltages
 OK? 
						

							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 LO level 
OK?
Locked?Ye s
Check FGU
Ye s
Trace IF signal 
from C3101 to 
Q3101. Check for 
bad XTAL filter.
No
Ye sIF
signal at Q3102 
collector?
Before replacing 
U3101, check 
U3101 voltages.
Ye s
Check for 
5VDC
Is 9V3 
present?
Check Supply Voltage 
circuitry. Check Q0681, 
U4211 and U0641.
No
No
No
Check U4501. 
Check varactor filter.
NoYe s
Ye s
Ye s
A
A
B
weak RFRF
Signal at 
C4009? 
						

							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  
9.1V DC
If U4201 Pin 2 is high,  
replace PCIC 
U4501,otherwise 
check controller and 
FGU
YES
NOTP4403 
>0.5V DC?Replace PCIC U4501
Check Forward Power 
Sense Circuit (D4451)
Check Forward Power 
Sense Circuit (D4451)
NO
YESPCIC U4501 
Pin 5 > 1V 
DC?
Check Power Setting, 
Tuning & Components 
between PCIC Pin 5 
and ASFIC (U0221) 
Pin 4 before replacing 
ASFIC
No or too low Power when keyed 
						

							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 
between U4402-2 Pin7 
and Q4421. Check 
Resistive Network at 
Pins 5 & 6 before 
replacing Q4421
YESDC 
Voltage at 
U4402-2 Pin 5 

						

							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 
Q4421 Gate 
>1V?
NOCheck Components 
between 
C4417  & Q4421
YESRF Voltage 
Q4441 Gate 
>4V?
NOCheck Components 
between 
Q4421  & Q4441
Check Components 
between Q4441  & 
Antenna Connector
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
Troubleshoot
ASFIC
Check voltage
on TP4531
Change
PCIC
Check R4409 &
 R4473 and go back
to top
     Check
MOSBIAS_2Check
ASFIC
Are D4471 &
D4472 OK?Change
D4471 &
D4472
NoNo
NoYe sYe s Ye s Ye sYe s
Ye s Ye s
Ye s
NoCheck
PCIC
Ye s
Change Q4421
Change Q4431
Ye s
Change U4401
Ye sDo visual check
on all components
No
Change Q4441
Troubleshoot
        VCO No
Check voltage
Check voltage
on Pin 4 U4501
   OK?
   OK?
   OK?
   OK?    OK?   OK?    OK? 
						

							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 VDC in 
Tx & 
						

							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 =180mVRMSat “-” Side of 
4.5VDC
at CR4321
If C4321 and R4321 are OK,
 then replace CR4321
Replace C4322
Replace C4325
NONO
YES
YES
If parts between  
R4402 & U4301 Pin10
are OK, replace U4301
TX VCO
RX VCO
Correct
ProblemVisual check
of board
OK?
Check runner 
between U4201 Pin 2 
and U4301 Pin 19
Is RF available 
If all parts from U4301 Pin 8
to Base of Q4332 are OK, 
replace U4301
If all parts associated 
with the pins are OK, 
replace Q4332
If all parts from collector
of Q4332 to TP4003 are
OK, Replace Q4332
Power OK but 
no modulation
Check parts from
R4402 to U4401 Pin16
If all parts 
associated 
with the pins 
are OK, 
replace U4301
YESYES
Make sure Synthesizer is 
working correctly and runner 
between U4201 Pin 28 and 
U4301 Pin 14 & and  is OK 4.5V DC 
OK ?
OK?
OK?
C4325  at U4301 Pin 14 & 18    4.5V DC 
OK ? at U4301 Pin 14&18    
NO