Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

Frequency Synthesis2-7
4.0 Frequency Synthesis
The frequency synthesizer subsystem, shown in Figure 2-3, consists of the reference oscillator 
crystal (Y1201), the Low Voltage Fractional-N synthesizer (LVFRAC-N, U1201), and the receive and 
transmit VCOs and buffers (Q1303 through Q1308 and associated components).
Figure 2-3 Low Band Synthesizer Block Diagram
4.1 Fractional-N Synthesizer 
The LVFRAC-N synthesizer IC (U1201) consists of a reference oscillator, pre-scaler, a 
programmable loop divider,...

2-8Frequency Synthesis
of 13 volts DC. This multiplier is driven by two 1.05 MHz clock signals from U1201 pins 15 and 14 
(VMULTI1 and VMULTI2) which are 180 degree out of phase.
Output LOCK (U1201-4) provides information about the lock status of the synthesizer loop. A high 
level at this output indicates a stable loop. A buffered output of the 16.8 MHz reference frequency is 
provided at pin 19.
The operating frequency of the synthesizer is loaded serially from the microprocessor via the data 
line...

Frequency Synthesis2-9
The VCOs, together with Fractional-N synthesizer U1201, generates the required frequencies for 
transmit and receive modes. The TRB line (U1201, pin 2) determines which VCO/buffer circuit is to 
be enabled. A high level on TRB will turn on the transistors in U1378 to turn on via R1376, applying 
the 8.3 volt VSF source to the receiver VCO and first buffer. The second buffer in each string 
operates from the 9V3 source and become active when RF is applied to their inputs. 
The RF...

2-10Frequency Synthesis
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 (U1201-45) 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...

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 U1103?Check Controller (in the case of no audio).
Or else go to “B” Ye s
No
Spray or inject 10.7MHz 
into XTAL Filter FL1102.
Audio heard?BYe s
No
Check 2nd LO 
(10.245MHz) at C1129. 
LO present?BYe s
 Check volt-
ages on 
U1103. OK?
Biasing OK?
No
No
A
Ye s
Check Q1106 bias 
for faults.
Replace Q1106.
Go to B
Ye s
No
Check cir-
cuitry...

3-2 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
IF Signal at 
pin 2 of 
U1051
No
RF Signal 
at pin 3 of 
U1051?
RF Signal at 
C1017?
No
RF Signal at 
C1013?
No
RF Signal at 
C1002?
No or 
Check harmonic filters J1401 and ant.switch 
Check preselector and RF 
amp.
Inject RF into J1401
No
Ye s
Check RF amp (Q1001) 
Stage.
Check filter between C1017 
& mixer U1051
Ye s
Check for detailed mixer.
Ye s
1st LO level 
OK?
Locked?Ye s
Check FGU...

Troubleshooting Flow Chart for Transmitter3-3
2.0 Troubleshooting Flow Chart for Transmitter  
No
 DC Voltage
@ Gate of
Q1401
NoYe s
              START
        No or Low 
  
  TX DC Voltage 
      @Drains of 
Q1402 &
Q1403
@ Cathode of 
D1401 &
D1402 DC Voltage
Drains of Q1402 &AC Voltages @
Q1403 both sine or
both distorted
Check 9T1 and
Diode Bias Circuit
Verify RF Continuity
   to gates of
Q1402 & Q1403
 
Check circuitry
between Q1402 &
Q1403 and 
Antenna Port
CheckMOSBIAS_1
Supply and
Feed Network...

3-4Troubleshooting Flow Chart for Synthesizer
3.0 Troubleshooting Flow Chart for Synthesizer
5V
 at pin 6 of 
CR1202
Is information
from uP U0101
correct?
Is U1201 Pin 47
at = 13VDC
Is U1377, Pin 2
4.5 VDC in TX?  (at 
VCO section)
Start
Vi s u a l  
check of the 
Board OK?Correct
Problem
Check 9.3V
Regulator
U0641
+9.3V at 
U1201
Pin 30?
Is 16.8MHz
Signal at
U1201 Pin 19?
Check Y1201, C1204, 
C1206,C1207, 
CR1201. & R1203
Are signals
at Pin’s 14 &
15 of U1201?
Check 
R1218
Check C3319
Is U1201 pin 2>4.5...

Troubleshooting Flow Chart for VCO3-5
4.0 Troubleshooting Flow Chart for VCO
LOW OR NO RF SIGNAL
           AT U1051
VISUAL CHECK
OF BOARD
OK?
8.5V DC AT 
U1378 PIN 3

3-6Troubleshooting Flow Chart for VCO
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