Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

UHF (450-520 MHz) Frequency Synthesis2-7
Figure 2-3 UHF Synthesizer Block Diagram
Output LOCK (U5201-4) provides information about the lock status of the synthesizer loop. A high 
level at this output indicates a stable loop. IC U5201 provides the 16.8 MHz reference frequency at 
pin 19.
The serial interface (SRL) is connected to the µP via data line DATA (U5201-7), clock line CLK 
(U5201-8), and chip enable line CSX (U5201-9).
DATA
CLK
CEX
MODIN
VCC, DC5V
XTAL1
XTAL2
WARP
PREIN
VCP
REFERENCE
OSCILLATOR...

2-8UHF (450-520 MHz) Frequency Synthesis
4.3 Voltage Controlled Oscillator (VCO)
The voltage controlled oscillator (VCO), shown in Figure 2-4, consists of a VCO buffer IC (VCOBIC, 
U5301), TX and RX tank circuits, external RX buffer stages, and modulation circuits.
The VCOBIC together with Fractional-N synthesizer (U5201) generates the required frequencies in 
both transmit and receive modes. The TRB line (U5301, pin 19) determines which tank circuits and 
internal buffers are to be enabled. A high level...

UHF (450-520 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, 
pin 41) is applied to the modulation circuits CR5321, R5321, R5322, and C5324. These modulate 
the TX VCO frequency via coupling capacitor C5321. Varactor CR5321 is biased for linearity from 
the VSF.
4.4 Synthesizer Operation
The synthesizer consists of a low voltage FRAC-N...

2-10UHF (450-520 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 40W Transmitter 3-3
2.0 Troubleshooting Flow Chart for 40W Transmitter 
Q5441 gate (63kohm)
and drain resistances
             (15kohm)Check
No
Ye s
Is drive from VCO
        >+4dBm?
Is voltage
drop across R5497
between 1V and 0.7V
when Tx power
 = 44W? No
No
Q5421 gate (12kohm)
and drain resistances
             (15kohm)CheckNo
PCIC_MOSBIAS_1        Check
No
No
Change
Q5473 
              START
        No power
  
  Is Vctrl
there? Is Q5473
   OK?
Check voltage
n pin 4,...

3-4Troubleshooting 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 VCO3-5
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...

3-6Troubleshooting Flow Chart for VCO
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