Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

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 (LVFRACN) IC,...

2-10Frequency 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 
No
Is Q5441 OK ?
Ye s
Is drive from VCO
        >+4dBm? NoIs voltage drop across
     R5497 >4.5V ?No
Check Q5431 gate(open)
and drain resistances
            (11kohm)NoCheck Q5421 gate(open)
and drain resistances
             (11kohm)No
PCIC_MOSBIAS_1        Check
No
No
Change
Q4573 
              START
        No power
  
  Is Vctrl
there? Is Q5573
   OK?
Check voltage
n U5501, pin 4 
Check voltage
on...

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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4-1
Section 4
UHF PCB/SCHEMATICS/PARTS LISTS
1.0 Allocation of Schematics and Circuit Boards
1.1 Controller Circuits
The UHF circuits are contained on the Printed Circuit Board (PCB) which also contains the 
Controller circuits. This Chapter shows the schematics for the UHF circuits only, refer to the 
Controller section for details of the related Controller circuits . The PCB component layouts and the 
Parts Lists in this Chapter show both the Controller and UHF circuit components. The UHF 
schematics...

4-2Allocation of Schematics and Circuit Boards
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