Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

UHF (403-470 MHz) Frequency Synthesis2-7
4.2 Fractional-N Synthesizer
The LVFRAC-N synthesizer IC (U4201) consists of a pre-scaler, a programmable loop divider, 
control divider logic, a phase detector, a charge pump, an A/D converter for low frequency digital 
modulation, a balance attenuator to balance the high frequency analogue modulation and low 
frequency digital modulation, a 13V positive voltage multiplier, a serial interface for control, and 
finally a super filter for the regulated 5 volts....

2-8UHF (403-470 MHz) Frequency Synthesis
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U4301), the TX 
and RX tank circuits, the external RX buffer stages, and the modulation circuitry.
Figure 2-4 UHF VCO Block Diagram
The VCOBIC together with Fractional-N synthesizer (U4201) generates the required frequencies in 
both  transmit and receive modes. The TRB line (U4301 pin 19) determines which tank circuits and 
internal buffers are...

UHF (403-470 MHz) Frequency Synthesis2-9
The external RX buffers (Q4332) are enabled by a high at U4201 pin 3 (AUX4) via transistor switch 
Q4333.  In TX mode the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U4201 
pin41) is applied modulation circuitry CR4321, R4321, R4322 and C4324, which modulates the TX 
VCO frequency via coupling capacitor C4321.  Varactor CR4321 is biased for linearity from VSF.
4.4 Synthesizer Operation
The complete synthesizer subsystem comprises mainly of low...

2-10UHF (403-470 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 
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,...

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 
Q4441 and RF Output, 
Antenna Switch 
D4471,D4472,Q4472, 
VR3471,Q3471>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...

3-4 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 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...

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 
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...

3-6Troubleshooting Flow Chart for Synthesizer
3.0 Troubleshooting Flow Chart for Synthesizer
5V
 at pin 6 of 
D4201
Is
information
from
 µP U0101
correct
?
Is
U4201 Pin 47
at = 13VDC
?
Is
U4301 Pin 19
4.5 VDC in TX?  
(at VCO section)
?
Sta rt
Visual 
check of the 
Board
OK?Correct
Problem
Check 5V
Regulator
U4211
+5V
at U4201
Pins
13 & 30
?
Is
16.8MHz
Signal at U4201 
Pin 19
?
Check
Y4261 / Y4262 and 
associated parts
Are
signals
at Pins 14 &15 
of U4201
?
Check 
R4201Check C4381
Is
U4201
Pin 2  >4.5...