Motorola Vhf Manual

VHF (136-174MHz) Transmitter Power Amplifier (PA) 45 W 2-11
5.6 Antenna Switch
The antenna switch consists of two PIN diodes, D3471 and D3472. In the receive mode, both diodes 
are off. Signals applied at the antenna jack J3401 are routed, via the harmonic filter, through 
network L3472, C3474 and C3475, to the receiver input. In the transmit mode, K9V1 turns on Q3471 
which enables current sink Q3472, set to 96 mA by R3473 and VR3471. This completes a DC path 
from PASUPVLTG, through L3473, D3471, L3477,...

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 
C3035?
No
RF Signal at 
T3001?
RF Signal at 
C3012?
No
RF Signal at 
C3008?
No
RF Signal at 
C3474?
No or 
Check Harmonic Filter 
J3401 and
Antenna Switch 
D3471,D3472,L3472
Check filter between C3474 
& C3008. Check tuning 
voltage at R3019
Inject RF into J3401
Is tuning 
voltage OK?
No
Ye s
Check RF amp 
(Q3001) Stage
Check filter between 
C3012 & T3001
Ye s
Check T3001, T3002, 
D3031, R3030-R3034, 
L3032,...

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 S3440
Check Components between 
Q3441 and RF Output, 
Antenna Switch 
D3471,D3472,Q3472 >500mA & 4A
1V
Short TP3403 to 
Ground
NO
YES
Voltage at 
TP3402 
rises?Check PA StagesNO
YES
PCIC U3501 
Pin 14 9.3V 
DC?Check 9.3 V Regulator 
U0641
NO
YESPCIC U3501 
Pin 16 >4V 
DCReplace PCIC U3501
NO
YESTP3404...

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 U3401>6 YESDC Voltage 
at U3501 
Pin 23 =0?
2-6DC Voltage 
at U3402-1 
Pin 1?
YES Pin 2 Voltage 
0.62 * 
Voltage at 
Pin 1?
If U3201 Pin 2 is high,  
replace PCIC
NOReplace U3401
YES NODC
Voltage at 
U3402-1 Pin 
3 = 8.8V?
Check S3440, 
R3442 and R3443
YES Pin 3 Voltage 
0.51 * 
Voltage at 
Pin 1?
NOReplace U3401
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 
TP3406?
YESRF Voltage 
at TP3401 
>100mV?
YESRF Voltage 
U3401 Pin 6 
>3V?
Supply
Replace Q3441
Check FGU (U3301)
NOCheck Components 
between TP3401  & 
C3417
NO YESASFIC  
U0221 Pin 6 
1-4V DC?
Check Bias Tuning 
before replacing ASFIC 
U0221
Check Components 
between ASFIC and 
Q3441 before repla-
cing Q3441
YESRF...

3-6TROUBLESHOOTING CHARTS
3.0 Troubleshooting Flow Chart for 45W Transmitter (Sheet 1 of 2)
Current in-
crease when 
keyed?
NO YESSTART
No or too low Power when keyed
Check Components between 
Q3441 and RF Output, Antenna 
Switch D3471,D3472>500mA & 5A
1V
>1V 4V 
DCReplace PCIC
U3501
NO
YESTP3404  
9.1V DC
If U3201 Pin 3 is high,  
replace PCIC 
U3501,otherwise 
check controller and 
FGU
YES
NO
TP3403 
>0.5V DC?Replace PCIC U3501Check Forward & Reverse 
Power Sense Circuitry 
(D3451 & D3452)
Check...

Troubleshooting Flow Chart for 45W Transmitter (Sheet 1 of 2) 3-7
3.1Troubleshooting Flow Chart for Transmitter (Sheet 2 of 2) 
Pin 2 
Voltage 0.62 
* Voltage at 
Pin 1?
NO
YES Check PA Stages
No or too low Power when keyed
NOYES
Replace U3401 Pin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
2-4VSupply
0V
Bias 1 DC 
Voltage at 
TP3406?
NO YES
PCIC U3501 
Pin 24 2-4V 
DC?
Check Bias Tuning be-
fore replacing 
PCIC U3501
Check Voltage at Pin 2 & 3 of U3401
Replace U3401
Replace Q3421
NO 0V
1-4VBias 2 DC 
Voltage...

3-8TROUBLESHOOTING CHARTS
4.0 Troubleshooting Flow Chart for Synthesizer
+5V at 
U3201 Pin’s
13 & 30? 5V
 at pin 6 of 
D3201
Is information
from µP U0101
correct?
Is U3201 
Pin 47
= 13VDC ?
Is U3301 Pin 19
4.5 VDC in TX?  
(at VCO section)
Start
Visual 
check of the 
Board OK?Correct
Problem
Check 5V
Regulator 
U3211
Is 16.8MHz
Signal at
U3201 Pin 
19?
Check
Y3261, Y3263  and 
associated Parts
Are signals
at Pin’s 14 &
15 of U3201?
Check 
R3201
Check C3319Is U3201 pin 2  
>4.5 VDC in Tx &