Motorola Gm Series Detailed 6864115b62 A Manual

							UHF (403-470MHz) Transmitter Power Amplifier (PA) 40W 2-9
5.0 UHF (403-470MHz) Transmitter Power Amplifier (PA) 40W
The radio’s 40 W PA is a four stage amplifier used to amplify the output from the VCOBIC to the radio 
transmit level. It consists of the following four stages in the line-up. The first stage is a LDMOS 
predriver (U4401) that is controlled by pin 4 of PCIC (U4501) via Q4473 (CNTLVLTG). It is followed 
by another LDMOS stage (Q4421), an LDMOS stage (Q4431) and a bipolar final stage (Q4441).
Figure 2-1 UHF Transmitter Block Diagram 
Device Q4401 is surface mounted. Q4421, Q4431 and Q4441 are directly attached to the heat sink.
5.1 Power Controlled Stage
The first stage (U4401) amplifies the RF signal from the VCO (TXINJ) and controls the output power 
of the PA. The output power of the transistor U4401 is controlled by a voltage control line feed from 
the PCIC pin4(U4501). The control voltage simultaneously varies the bias of two FET stages within 
U4401. This biasing point determines the overall gain of U4401 and therefore its output drive level to 
Q4421, which in turn controls the output power of the PA. 
In receive mode the voltage control line is at ground level and turns off Q4473 which in turn switches 
off the biasing voltage to U4401.
5.2 Pre-Driver Stage
The next stage is a 13dB gain LDMOS device (Q4421) which requires a positive gate bias and a 
quiescent current flow for proper operation. The voltage of the line PCIC_MOSBIAS_1 is set in 
transmit mode by PCIC pin 24 and fed to the gate of Q4421 via the resistive network R4480, R4416 
and R4415. The bias voltage is tuned in the factory.PCIC
Pin Diode 
Antenna 
Switch
RF JackAntenna
Harmonic 
Filter
PowerSensePA-FinalStagePADriver From VCOControlledStage
VcontrolBias 1Bias 2
To Microprocessor
Temperature
Sense SPI BUS
ASFIC_CMP
PA
PWR
SET
To Microprocessor
PreDriver 
						

							2-10THEORY OF OPERATION
5.3 Driver Stage
The following stage is an enhancement-mode N-Channel MOSFET device (Q4431) providing a gain 
of 10dB. This device also requires a positive gate bias and a quiescent current flow for proper 
operation. The voltage of the line Bias_2_UHF_PA_1 is set in transmit mode by the ASFIC and fed to 
the gate of Q4431 via the resistive network R4632, R4631, R4485 and R4486. This bias voltage is 
also tuned in the factory. If the transistor is replaced, the bias voltage must be tuned using the 
Customer Programming Software (CPS). Care must be taken not to damage the device by exceeding 
the maximum allowed bias voltage. The device’s drain current is drawn directly from the radio’s DC 
supply voltage input, A+, via L4421.
5.4 Final Stage
The final stage uses the bipolar device Q4441. The device’s collector current is also drawn from the 
radio’s DC supply voltage input. To maintain class C operation, the base is DC-grounded by a series 
inductor (L4441) and a bead (L4440). A matching network consisting of C4441-C4444, C4491 and 
two striplines transforms the impedance to 50 Ohms and feeds the directional coupler.
5.5 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 PCIC. The PCIC 
controls the gain of stage U4401 as necessary to hold this voltage constant, thus ensuring the 
forward power out of the radio to be held to a constant value.
5.6 Antenna Switch
The antenna switch consists of two PIN diodes, D4471 and D4472. In the receive mode, both 
diodes are off. Signals applied at the antenna jack J4401 are routed, via the harmonic filter, through 
network L4472, C4474 and C4475, to the receiver input. In the transmit mode, K9V1 turns on 
Q4471 which enables current sink Q4472, set to 96 mA by R4511 and VR4471. This completes a 
DC path from PASUPVLTG, through L4437, D4471, L4472, D4472, L4473, R4496 and the current 
sink, to ground. Both diodes are forward biased into conduction. The transmitter RF from the 
directional coupler is routed via D4471 to the harmonic filter and antenna jack. D4472 also 
conducts, shunting RF power and preventing it from reaching the receiver port (RXIN). L4472 is 
selected to appear as a broadband Lambda/4 wave transmission line, making the short circuit 
presented by D4472 appear as an open circuit at the junction of D4472 and the receiver path.
5.7 Harmonic Filter
Inductors L4491, L4492, L4493 and capacitors C4448, C4492,C4494, C4496 and C4498 form a 
low-pass filter to attenuate harmonic energy of the transmitter to specifications level. R4491 is used 
to drain electrostatic charge that might otherwise build up on the antenna.  The harmonic filter also 
prevents high level RF signals above the receiver passband from reaching the receiver circuits, 
improving spurious response rejection. 
						

							UHF (403-470MHz) Transmitter Power Amplifier (PA) 40W 2-11
5.8 Power Control
The transmitter uses the Power Control IC (PCIC, U4501) to control the power output of the radio. A 
portion of the forward RF power from the transmitter is sampled by the bi-directional coupler and 
rectified, to provide a DC voltage to the RFIN port of the PCIC (pin 1) which is proportional to the 
sampled RF power. 
The PCIC has internal digital to analog converters (DACs) which provide the reference voltage of the 
control loop. The reference voltage level is programmable through the SPI line of the PCIC. This 
reference voltage is proportional to the desired power setting of the transmitter, and is factory 
programmed at several points across the frequency range of the transmitter to offset frequency 
response variations of the transmitter s power detector circuitry.
The PCIC provides a DC output voltage at pin 4 (INT) which is 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 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 the PCIC, control the 
transmitter power-rise (key-up) and power-decay (de-key) characteristic to minimize splatter into 
adjacent channels.
U4502 is a temperature-sensing device, which monitors the circuit board temperature in the vicinity 
of the transmitter driver and final devices, and provides a dc voltage to the PCIC (TEMP, pin 29) 
proportional to temperature. If the DC voltage produced exceeds the set threshold in the PCIC, the 
transmitter output power will be reduced so as to reduce the transmitter temperature. 
						

							2-12THEORY OF OPERATION 
						

							Chapter 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 defectCheck circuitry around Y3101 Re-
place Y3101 if defectVoltages
 OK? 
						

							3-2TROUBLESHOOTING CHARTS
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 filter
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, R4052, L4008.
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, 
U4211 and U0641.
No
No
No
Check U4501. 
Check varactor filter.
NoYe s
Ye s
Ye s
A
A
B
weak RFRF
Signal at 
C4009? 
						

							Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 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 
Q4441 and RF Output, 
Antenna Switch 
D4471,D4472,Q4472, >500mA & 4A
1V
Short TP4403 to 
Ground
NO
YES
Voltage at 
TP4402 
rises?Check PA StagesNO
YES
PCIC U4501 
Pin 14 9.3V 
DC?Check 9.3 V Regulator 
U0641
NO
YESPCIC U4501 
Pin 16 >4V 
DCReplace PCIC U4501
NO
YESTP4404  
9.1V DC
If U4201 Pin 2 is high,  
replace PCIC 
U4501,otherwise 
check controller and 
FGU
YES
NOTP4403 
>0.5V DC?Replace PCIC U4501
Check Forward Power 
Sense Circuit (D4451)
Check Forward Power 
Sense Circuit (D4451)
NO
YESPCIC U4501 
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 
						

							3-4TROUBLESHOOTING CHARTS
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 U4401>6 YESDC Voltage 
at U4501 
Pin 23 =0?
2-6DC Voltage 
at U4402-1 
Pin 1?
YESPin 2
Voltage 0.62 
* Voltage at 
Pin 1?
If U4201 Pin 2 is high,  
replace PCIC
NOReplace U4401
YES NODC 
Voltage at 
U4402-1 Pin 
3 = 8.8V?
Check S4440, 
R4442 and R4443
YESPin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
NOReplace U4401
6V
Check Components 
between U4402-2 Pin7 
and Q4421. Check 
Resistive Network at 
Pins 5 & 6 before 
replacing Q4421
YESDC 
Voltage at 
U4402-2 Pin 5 

						

							Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 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 
TP4406?
YESRF Voltage 
at TP4401 
>100mV?
YESRF Voltage 
U4401 Pin 6 
>3V?
Supply
Replace Q4441
Check FGU (U4301)
NOCheck Components 
between 
TP4401  &C4417
NO YESASFIC  
U0221 Pin 6 
1-4V DC?
Check Bias Tuning 
before replacing ASFIC 
U0221
Check Components 
between ASFIC and 
Q4441 before 
replacing Q4441
YESRF Voltage 
Q4421 Gate 
>1V?
NOCheck Components 
between 
C4417  & Q4421
YESRF Voltage 
Q4441 Gate 
>4V?
NOCheck Components 
between 
Q4421  & Q4441
Check Components 
between Q4441  & 
Antenna Connector
Voltage 
						

							3-6TROUBLESHOOTING CHARTS
3.0 Troubleshooting Flow Chart for UHF 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
No
No
Change
Q4473 
              START
        No power
  
  Is Vctrl
there? Is Q4473
   OK?
Check voltage
on Pin 5 U4501
Check R4422-5
and go back to top
Troubleshoot
ASFIC
Check voltage
on TP4531
Change
PCIC
Check R4409 &
 R4473 and go back
to top
     Check
MOSBIAS_2Check
ASFIC
Are D4471 &
D4472 OK?Change
D4471 &
D4472
NoNo
NoYe sYe s Ye s Ye sYe s
Ye s Ye s
Ye s
NoCheck
PCIC
Ye s
Change Q4421
Change Q4431
Ye s
Change U4401
Ye sDo visual check
on all components
No
Change Q4441
Troubleshoot
        VCO No
Check voltage
Check voltage
on Pin 4 U4501
   OK?
   OK?
   OK?
   OK?    OK?   OK?    OK?