Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

Frequency Synthesis2-7
A voltage of 5V applied to the super filter input (U3201 pin 30) supplies an output voltage of 4.5 Vdc 
(VSF) at pin 28. It supplies the VCO, VCO modulation bias circuit (via R3363) and the synthesizer 
charge pump resistor network (R3251, R3252). The synthesizer supply voltage is provided by the 5V 
regulator U3211.
In order to generate a high voltage to supply the phase detector (charge pump) output stage at pin 
VCP (U3201-47), a voltage of 13 Vdc is being generated by the...

2-8Frequency Synthesis
The VCOBIC together with the Fractional-N synthesizer (U3201) generates the required frequencies 
in both the transmit and receive modes. The TRB line (U3301, pin 19) determines which tank circuits 
and internal buffers are to be enabled. A high level on TRB enables the TX tank and TX output (pin 
10), and a low enables the RX tank and RX output (pin 8). A sample of the signal from the enabled 
RF output is routed from U3301, pin 12 (PRESC_OUT), via a low pass filter, to U3201, pin...

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 
C3035?
No
RF Signal at 
T3001?
RF Signal at 
C3012?
No
RF Signal at 
C3008?
No
RF Signal at 
C3474?
No or 
Check Harmonic Filter 
J3401 and
Antenna Switch 
D3471,D3472,L3472
Check filter between C3474 
& C3008. Check tuning 
voltage at R3019
Inject RF into J3401
Is tuning 
voltage OK?
No
Ye s
Check RF amp 
(Q3001) Stage
Check filter between 
C3012 & T3001
Ye s
Check T3001, T3002, 
D3031,...

Troubleshooting Flow Chart for 45W Transmitter 3-3
2.0 Troubleshooting Flow Chart for 45W Transmitter  (Sheet 1 of 2)
Current in-
crease when 
keyed?
NO YESSTART
No or too low Power when keyed
Check Components between 
Q3441 and RF Output, Antenna 
Switch D3471,D3472>500mA & 5A
1V
>1V 4V 
DCReplace PCIC
U3501
NO
YESTP3404  
9.1V DC
If U3201 Pin 3 is high,  
replace PCIC 
U3501,otherwise 
check controller and 
FGU
YES
NO
TP3403 
>0.5V DC?Replace PCIC U3501Check Forward & Reverse 
Power Sense Circuitry...

3-4 Troubleshooting Flow Chart for 45W Transmitter
2.1Troubleshooting Flow Chart for 45W Transmitter (Sheet 2 of 2)
Pin 2 
Voltage 0.62 
* Voltage at 
Pin 1?
NO
YES Check PA Stages
No or too low Power when keyed
NOYES
Replace U3401 Pin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
2-4VSupply
0V
Bias 1 DC 
Voltage at 
TP3406?
NO YES
PCIC U3501 
Pin 24 2-4V 
DC?
Check Bias Tuning be-
fore replacing 
PCIC U3501
Check Voltage at Pin 2 & 3 of U3401
Replace U3401
Replace Q3421
NO 0V
1-4VBias 2 DC 
Voltage at 
TP3407?...

Troubleshooting Flow Chart for Synthesizer3-5
3.0 Troubleshooting Flow Chart for Synthesizer
+5V at 
U3201 Pins
13 & 30? 5V
 at pin 6 of 
D3201
Is information
from µP U0101
correct?
Is U3201 
Pin 47
= 13VDC ?
Is U3301 Pin 19
4.5 VDC in TX?  
(at VCO section)
Sta rt
Visual 
check of the 
Board OK?Correct
Problem
Check 5V
Regulator 
U3211
Is 16.8MHz
Signal at
U3201 Pin 
19?
Check
Y3261, Y3263 and 
associated parts
Are signals
at Pins 14 &
15 of U3201?
Check 
R3201
Check C3319Is U3201 pin 2  
>4.5 VDC in Tx...

3-6Troubleshooting Flow Chart for VCO
4.0 Troubleshooting Flow Chart for VCO
Are Q3301
Base at 0.7V 
Collector at 4.5V 
Emitter at 110mV
Are Q3304
Base at 2.4V 
Collector at 4.5V 
Emitter at 1.7VAre U3301 Pins
13 at 4.4V
15 at 1.1V
10 at 4.5V
16 at 1.9V
Low or no RF Signal
at TP3001
Visual check
of board
OK?
35mV DC at
U3301 Pin 19
NO
YES
at base of Q3301
NO
NO
NO
NONO YES
YES
YES
YESYESLow or no RF Signal
at input to PA5V DC at U3301
Pin 14 & 18 OK ?
4.8V DC at
U3301 Pin 19
Is RF available 
at TP3401...

4-1
Section 4
VHF PCB/SCHEMATICS/PARTS LIST
1.0 Allocation of Schematics and Circuit Boards
1.1 Controller Circuits
The VHF circuits are contained on the Printed Circuit Board (PCB) which also contains the 
Controller circuits. This Chapter shows the schematics for the VHF 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 VHF circuit components. The VHF 
schematics...

4-2Allocation of Schematics and Circuit Boards
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