Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

Transmitter Power Amplifier (PA) 40 W2-5
3.5 Bi-Directional Coupler
The Bi-directional coupler is a microstrip printed circuit, which couples a small amount of the forward 
and reverse power of the RF power from Q4441. The coupled signal is rectified to an output power 
proportional dc voltage by the diodes D4451 & D4452 and sent to the RFIN of the PCIC. The PCIC 
controls the gain of stage U4401 as necessary to hold this voltage constant. This ensures the 
forward power out of the radio is held to a...

2-6Frequency Synthesis
The PCIC provides a dc output voltage at pin 4 (INT) and applied as CNTLVLTG to the power-adjust 
input pin of the first transmitter stage U4401. This adjusts the transmitter power output to the 
intended value. Variations in forward or reflected transmitter power cause the dc voltage at pin 1 to 
change, and the PCIC adjusts the control voltage above or below its nominal value to raise or lower 
output power.
Capacitors C4502-4, in conjunction with resistors and integrators within...

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 balanced attenuator to balance the high frequency analog 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.
A voltage of 5V...

2-8Frequency 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 circuits.
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 to be enabled. A high level on TRB enables TX tank and...

Frequency Synthesis2-9
4.4 Synthesizer Operation
The complete synthesizer subsystem comprises mainly of a low voltage FRAC-N (LVFRACN) IC, 
Reference Oscillator (crystal oscillator with temperature compensation), charge pump circuits, loop 
filter circuits, and dc supply. The output signal (PRESC_OUT) of the VCOBIC (U4301, pin12) is fed 
to of U4201, pin 32 (PREIN) via a low pass filter (C4229,L4225,C4226) which attenuates harmonics 
and provides correct level to close the synthesizer loop.
The...

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 
T4051?
RF
Signal at 
C4015?
No
No
RF
Signal at 
C4025?
No or 
Check harmonic filters
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 40W Transmitter 3-3
2.0 Troubleshooting Flow Chart for 40W Transmitter 
No
Is Q4441 OK ?
Ye s
Is drive from VCO
        >+4dBm? NoIs voltage drop across
     R4497 >4.5V ?No
Check Q4431 gate(open)
and drain resistances
            (11kohm)NoCheck Q4421 gate(open)
and drain resistances
             (11kohm)No
        Check
PCIC_MOSBIAS_1
NoNo
Change
Q4573 
              START
        No power
  
  Is Vctrl
there? Is Q4573
   OK?
Check voltage
on pin 4 U4501
Check voltage
on...

3-4Troubleshooting 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)
Start
Vi s u a l  
check of the 
Board OK?Correct
Problem
Check 5V
Regulator
U4211
+5V at U4201
Pin’s
13 & 30?
Is 16.8MHz
Signal at
U4201 Pin 19?
Check Y4261, C4261, 
C4262, C4263, D4261 
& R4261
Are signals
at Pin’s 14 &
15 of U4201?
Check 
R4201
Check C4381
Is U4201 pin 2...