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
 VOLTAGE
MULTIPLIER
DATA (U0101 PIN 100)
CLOCK (U0101 PIN 1)
CSX (U0101 PIN 2)
MOD IN (U0221 PIN 40)
+5V (U4211 PIN 1)7
8
9
10
13, 30
23
24
25
32
47
VMULT2 VMULT1BIAS1 SFOUTAUX3 AUX4 IADAPTIOUTGND FREFOUTLOCK4
19
6, 22, 33, 44
43
45
3
2
28
       14
        1540FILTERED 5VSTEERING LOCK (U0101 PIN 56)
PRESCALER INFREF (U0221 PIN 34)
39 BIAS2
41
 48 5, 20, 34, 36
+5V (U4211 PIN 1)
AUX1 VDD, DC5VMODOUT
U5201 
LOW VOLTAGEFRACTIONAL-N
SYNTHESIZER
AUX21 (NU)
BWSELECTVCO Bias
TRB
To IF
SectionTX RF INJECTION
(1ST STAGE OF PA)LO RF INJECTION
VOLTAGE 
CONTROLLED 
OSCILLATORLINE
2-POLE
LOOP
FILTER 
						

							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 on TRB enables TX tank and TX output (pin 10), and 
a low enables RX tank and RX output (pin 8). A sample of the signal from the enabled output is 
routed from U5301, pin 12 (PRESC_OUT), via a low pass filter of U5201, pin 32 (PREIN).
A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR5311 tunes the full 
TX frequency range (TXINJ) from 450 MHz to 520 MHz, and at varactor diodes CR5301, CR5302, 
and CR5303 tunes the full RX frequency range (RXINJ) from 405 MHz to 475 MHz. The tank circuits 
uses the Hartley configuration for wider bandwidth. For the RX tank circuit, external transistor 
Q5301 is used in conjunction with the internal transistor for better side-band noise.
Figure 2-4 UHF VCO Block Diagram
 
Presc
RX
TXMatching
NetworkLow Pass
    Filter
Attenuator Pin8
Pin14
Pin10(U5201 Pin28)
VCC Buffers
TX RF Injection U5201 Pin 32 AUX3 (U5201 Pin2)
Prescaler Out
Pin 12 Pin 19 Pin 20
      TX/RX/BS
Switching Network
U5301
VCOBIC
       Rx
Active Bias
      Tx
Active Bias
Pin2
Rx-I adjustPin1
Tx-I adjustPins 9,11,17
Pin18Vsens
Circuit Pin15Pin16 RX VCO
 Circuit
TX VCO
 Circuit RX Tank
TX TankPin7
Vcc-Superfilter
Collector/RF in
Pin4
Pin5
Pin6
RX
TX
(U5201 Pin28)Rx-SW
Tx-SW
Vcc-Logic
(U5201 Pin28) Steer Line 
Voltage 
(VCTRL)Pin13
Pin3TRB IN
LO RF INJECTION
Q4301
Q4332 
						

							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 (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 (U5301, pin12) is fed to of U5201, pin 32 (PREIN) 
via a low pass filter (C5229,L5225,and C5226) which attenuates harmonics and provides correct 
level to close the synthesizer loop.
The pre-scaler in the synthesizer (U5201) is a dual modulus pre-scaler with selectable divider ratios. 
The 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 routed to the charge pump. The charge 
pump outputs a current at U5201, pin 43 (IOUT). The loop filter (consisting of R5221-R5223, C5221-
C5225, and L5221) transforms this current into a voltage that is applied to varactor diodes CR5311 
for transmit, CR5301, CR5302 and 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 transistion 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) which is routed to one of the µP´s ADCs input 
U101-56. From the voltage the µP determines whether LOCK is active.
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 frequency path) and the balanced attenuator 
(high frequency path). The A/D converter converts the low frequency analog modulating signal into 
a digital code which 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 and C5325. 
						

							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 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 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, U5501 
Check voltage
on pin 5, U5501
Check R5422-5
and go back to top
Troubleshoot
ASFIC
Change
PCIC
Check R5409 and
 R5473 and go back
to top
     Check
                
MOSBIAS_2/
MOSBIAS_3Check
ASFIC
Are D5471 &
D5472 OK?Change
D5471 &
D5472
No NoNo
Ye sYe sYe s Ye s Ye sYe s
Ye s Ye s
No
NoCheck
PCIC
Ye s
Change Q5421
Change Q5441
Change U5401
Ye sDo visual check
on all components
No
Troubleshoot
        VCO
Check voltage
on TP5531
Check if Pressure 
Pad closes S5440
Ye s 
						

							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 VDC in 
Tx & 
						

							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
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 
						

							3-6Troubleshooting Flow Chart for VCO
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