Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

							UHF (450-527 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 
pin41) is applied modulation circuitry CR5321, R5321, R5322 and C5324, which modulates the TX 
VCO frequency via coupling capacitor C5321.  Varactor CR5321 is biased for linearity from VSF.
4.4 Synthesizer Operation
The complete synthesizer subsystem comprises mainly of low voltage FRAC-N (LVFRACN) IC, 
Reference Oscillator (crystal oscillator with temperature compensation), charge pump circuitry, loop 
filter circuitry and DC supply. The output signal PRESC_OUT of the VCOBIC (U5301 pin 12) is fed 
to pin 32 of U5201 (PREIN) via a low pass filter (C5229, L5225) which attenuates harmonics and 
provides the correct level to close the synthesizer loop.
The pre-scaler in the synthesizer (U5201) is basically a dual modulus pre-scaler with selectable 
divider ratios. This divider ratio of the pre-scaler is controlled by the loop divider, which in turn 
receives its inputs via the SRL. The output of the pre-scaler is applied to the loop divider. The output 
of the loop divider is connected to the phase detector, which compares the loop divider´s output 
signal with the reference signal.The reference signal is generated by dividing down the signal of the 
reference oscillator (Y5261 or Y5262).
The output signal of the phase detector is a pulsed DC signal which is routed to the charge pump. 
The charge pump outputs a current at pin 43 of U5201 (IOUT). The loop filter (which consists of 
R5221-R5223, C5221-C5225,L5221) transforms this current into a voltage that is applied to the 
varactor diodes CR5311 for transmit, CR5301, CR5302 & CR5303 for receive and alters the output 
frequency of the VCO .The current can be set to a value fixed in the LVFRAC-N IC or to a value 
determined by the currents flowing into BIAS 1 (U5201-40) or BIAS 2 (U5201-39). The currents are 
set by the value of R5251 or R5252 respectively. The selection of the three different bias sources is 
done by software programming.
To reduce synthesizer lock time when new frequency data has been loaded into the synthesizer the 
magnitude of the loop current is increased by enabling the IADAPT  (U5201-45) for a certain 
software programmable time (Adapt Mode). The adapt mode timer is started by a low to high 
transient of the CSX line. When the synthesizer is within the lock range the current is determined 
only by the resistors connected to BIAS 1, BIAS 2, or the internal current source. A settled 
synthesizer loop is indicated by a high level of signal LOCK (U5201-4). 
The LOCK (U5201-4) signal is routed to one of the µP´s ADCs input U101-56. From the voltage the 
µP determines whether LOCK  is active. In order to modulate the PLL the two spot modulation 
method is utilized. Via pin 10 (MODIN) on U5201 the audio signal is applied to both the A/D 
converter (low freq path) as well as the balance attenuator (high freq path). The A/D converter 
converts the low frequency analogue modulating signal into a digital code that is applied to the loop 
divider, thereby causing the carrier to deviate. The balance attenuator is used to adjust the VCO’s 
deviation sensitivity to high frequency modulating signals. The output of the balance attenuator is 
present at the MODOUT port (U5201-41) and connected to the VCO modulation diode CR5321 via 
R5321, C5325. 
						

							2-10UHF (450-527 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 U3101.
Replace 
U3101 if defect
Check circuitry around Y3101. 
Replace Y3101 if defectVoltages
 OK? 
						

							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, R5052, L5008.
Ye s
1st LO level 
OK?
Locked?Ye s
Check FGU
Ye s
Trace IF signal 
from C3101 to 
Q3101. Check for 
bad XTAL filter.
No
Ye sIF
signal at Q3102 
collector?
Before replacing 
U3101, check 
U3101 voltages.
Ye s
Check for 
5VDC
Is 9V3 
present?
Check Supply Voltage 
circuitry. Check Q0681, 
U5211 and U0641.
No
No
No
Check U5501. 
Check varactor filter.
NoYe s
Ye s
Ye s
A
A
B
weak RFRF
Signal at 
C5009? 
						

							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 
Q5441 and RF Output, 
Antenna Switch 
D5471,D5472,Q5472, 
VR3471,Q3471>500mA & 4A
1V
Short TP5403 to 
Ground
NO
YES
Voltage at 
TP5402 
rises?Check PA StagesNO
YES
PCIC U5501 
Pin 14 9.3V 
DC?Check 9.3 V Regulator 
U0641
NO
YESPCIC U5501 
Pin 16 >4V 
DCReplace PCIC U5501
NO
YESTP5404  
9.1V DC
If U5201 Pin 2 is high,  
replace PCIC 
U5501,otherwise 
check controller and 
FGU
YES
NOTP5403 
>0.5V DC?Replace PCIC U5501
Check Forward Power 
Sense Circuit (D5451)
Check Forward Power 
Sense Circuit (D5451)
NO
YESPCIC U5501 
Pin 5 > 1V 
DC?
Check Power Setting, 
Tuning & Components 
between PCIC Pin 5 
and ASFIC (U0221) 
Pin 4 before replacing 
ASFIC
No or too low Power when keyed 
						

							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 U5401>6 YESDC Voltage 
at U5501 
Pin 23 =0?
2-6DC Voltage 
at U5402-1 
Pin 1?
YESPin 2
Voltage 0.62 
* Voltage at 
Pin 1?
If U5201 Pin 2 is high,  
replace PCIC
NOReplace U5401
YES NODC 
Voltage at 
U5402-1 Pin 
3 = 8.8V?
Check S5440, 
R5442 and R5443
YESPin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
NOReplace U5401
6V
Check Components 
between U5402-2 Pin 7 
and Q5421. Check 
Resistive Network at 
Pins 5 & 6 before 
replacing Q5421
YESDC 
Voltage at 
U5402-2 Pin 5 

						

							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 
TP5406?
YESRF Voltage 
at TP5401 
>100mV?
YESRF Voltage 
U5401 Pin 6 
>3V?
Supply
Replace Q5441
Check FGU (U5301)
NOCheck Components 
between 
TP5401  &C5417
NO YESASFIC  
U0221 Pin 6 
1-4V DC?
Check Bias Tuning 
before replacing ASFIC 
U0221
Check Components 
between ASFIC and 
Q5441 before 
replacing Q5441
YESRF Voltage 
Q5421 Gate 
>1V?
NOCheck Components 
between 
C5417  & Q5421
YESRF Voltage 
Q5441 Gate 
>4V?
NOCheck Components 
between 
Q5421  & Q5441
Check Components 
between Q5441  & 
Antenna Connector
Voltage 
						

							3-6Troubleshooting 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 VDC in 
Tx & 
						

							Troubleshooting Flow Chart for VCO3-7
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
Audio =180mVrmsat “-” Side of 
4.5VDC
at CR5321
If C5321 and R5321 are OK,
 then replace CR5321
Replace C5322
Replace C5325
NONO
YES
YES
 
TX VCO
RX VCO
Correct
ProblemVisual check
of board
OK?
Check runner 
between U5201 Pin 2 
and U5301 Pin 19
Is RF available 
If all parts from U5301 Pin 8
to Base of Q5332 are OK, 
replace U5301
If all parts associated 
with the pins are OK, 
replace Q5332
If all parts from collector
of Q5332 to TP5003 are
OK, Replace U5301
Power OK but 
no modulation
If all parts from U5301 Pin 10
U5401 Pin 16 are OK,
replace U5301
Replace 
Q5311
YESYES
Make sure Synthesizer is 
working correctly and runner 
between U5201 Pin 28 and 
U5301 Pin 14 & 18 are OK 4.5V DC 
OK ?
OK?
OK?
C5325  at U5301 Pin 14 & 18    4.5V DC 
OK ? at U5301 Pin 14 &18    
NO
Pin 16
If R5361 and 
L5361 are OK, 
replace U5301 
						

							3-8Troubleshooting Flow Chart for VCO
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