Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

UHF (450-527 MHz) Frequency Synthesis2-9
The external RX buffers (Q5332) are enabled by a high at U5201 pin 3 (AUX4) via transistor switch 
Q5333.  In TX mode the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U5201 
pin41) is applied modulation circuitry CR5321, R5321, R5322 and C5324, which modulates the TX 
VCO frequency via coupling capacitor C5321.  Varactor CR5321 is biased for linearity from VSF.
4.4 Synthesizer Operation
The complete synthesizer subsystem comprises mainly of low...

2-10UHF (450-527 MHz) Frequency Synthesis
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3-1
Section 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...

3-2Troubleshooting Flow Chart for Receiver
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
IF Signal at 
C3101?
No
RF 
Signal at 
T5051?
RF
Signal at 
C5015?
No
No
RF
Signal at 
C5025?
No or 
Check harmonic filter
L5491-L5493, C5492, J5401
and ant. switch
D5471, D5472, L5472.
Check filter between 
C5025 & C5009. 
Check tuning voltage 
at R5060.
Inject RF into J5401
Is
tuning voltage
OK?
No
Ye s
Check RF amp (Q5003) 
Stage.
Check filter between 
C5015 & T5051.
Ye s
Check T5051, T5052, 
D5051,...

Troubleshooting Flow Chart for 25W Transmitter 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 
Q5441 and RF Output, 
Antenna Switch 
D5471,D5472,Q5472, 
VR3471,Q3471>500mA & 4A
1V
Short TP5403 to 
Ground
NO
YES
Voltage at 
TP5402 
rises?Check PA StagesNO
YES
PCIC U5501 
Pin 14 9.3V 
DC?Check 9.3 V Regulator 
U0641
NO
YESPCIC U5501 
Pin 16 >4V 
DCReplace PCIC U5501
NO
YESTP5404...

3-4 Troubleshooting Flow Chart for 25W Transmitter
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 U5401>6 YESDC Voltage 
at U5501 
Pin 23 =0?
2-6DC Voltage 
at U5402-1 
Pin 1?
YESPin 2
Voltage 0.62 
* Voltage at 
Pin 1?
If U5201 Pin 2 is high,  
replace PCIC
NOReplace U5401
YES NODC 
Voltage at 
U5402-1 Pin 
3 = 8.8V?
Check S5440, 
R5442 and R5443
YESPin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
NOReplace...

Troubleshooting Flow Chart for 25W Transmitter 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 
TP5406?
YESRF Voltage 
at TP5401 
>100mV?
YESRF Voltage 
U5401 Pin 6 
>3V?
Supply
Replace Q5441
Check FGU (U5301)
NOCheck Components 
between 
TP5401  &C5417
NO YESASFIC  
U0221 Pin 6 
1-4V DC?
Check Bias Tuning 
before replacing ASFIC 
U0221
Check Components 
between ASFIC and 
Q5441 before 
replacing Q5441
YESRF Voltage 
Q5421 Gate...

3-6Troubleshooting Flow Chart for Synthesizer
3.0 Troubleshooting Flow Chart for Synthesizer
5V
 at pin 6 of 
D5201
Is
information
from
 µP U0101
correct
?
Is
U5201 Pin 47
at = 13VDC
?
Is
U5301 Pin 19
4.5 VDC in TX?  
(at VCO section)
?
Sta rt
Visual 
check of the 
Board
OK?Correct
Problem
Check 5V
Regulator
U5211
+5V
at U5201
Pins
13 & 30
?
Is
16.8MHz
Signal at U5201 
Pin 19
?
Check
Y5261 / Y5262 and 
associated parts
Are
signals
at Pins 14 &15 
of U5201
?
Check 
R5201Check C5381
Is
U5201
Pin 2  >4.5...

Troubleshooting Flow Chart for VCO3-7
4.0 Troubleshooting Flow Chart for VCO
Are Q5332
Base at 0.7V 
Collector at 4.5V 
Emitter at 110mV
Are Q5301
Base at 2.4V 
Collector at 4.5V 
Emitter at 1.7VAre Q5311 
Base = 1.9V
Collector = 4.5V
Emitter = 1.3V
Low or no RF Signal
at TP5003
Visual check
of board
OK?
35mV DC at
U5301 Pin 19
NO
YES
Replace Q5301
at base of Q5332
NO
NO
NO
NO YES
YES
YESYESLow or no RF Signal
at input to PA
4.8V DC at
U5301 Pin 19
Is RF available 
at U5401
YES
YESYES YES NO
NO
NO
NO
NO...

3-8Troubleshooting Flow Chart for VCO
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