VAL AVIONICS LTD
AWOS 2000
VHF Transmitter
Maintenance and Repair
Manual
Revision 1
April 2012
P/N 172211
Page 1: ...VAL AVIONICS LTD AWOS 2000 VHF Transmitter Maintenance and Repair Manual Revision 1 April 2012 P N 172211 ...
Page 2: ...embly 4 1 2 1 1 Microcontroller 4 1 2 1 2 Power Supply Circuits 5 1 2 1 3 Modulation Control 5 1 2 1 4 RF TX Generator 6 1 2 2 Transmitter Board 7 2 Troubleshooting 8 2 1 Troubleshooting Equipment Required 8 2 2 Initial Troubleshooting Operations 8 2 3 Power Supply Check 8 3 Disassembly Instructions 9 3 1 Removal of the Covers 9 3 2 Board and Module Disassembly 9 3 2 1 Main Board Removal 9 3 2 4 T...
Page 3: ...tches to control the active frequency and three adjustments for controlling power modulation and frequency The unit case is constructed from milled aluminum the boards are constructed using high quality materials and use the latest techniques in manufacturing technology In order to achieve the desired reliability size and power requirements surface mounted components are used extensively Specializ...
Page 4: ...board assembly contains the microcontroller power supply audio circuitry and RF TX generator 1 2 1 1 Microcontroller This board contains a microchip PIC16F818 microcontroller featuring 1kB of EEPROM memory running at 8MHz Other circuits on the board are used for input output functions such as controlling the frequency and controlling the transmitter boards The block diagram in Figure 2 below shows...
Page 5: ...XMIT Key XMIT Power VCO Enable To Transmitter J3 X1 X3 X5 To J4 Audio Input Modulation AGC Sense From TX XMIT Enable Figure 2 AWOS2000 Mainboard Block Diagram 1 2 1 2 Power Supply Circuits The power supply section of the main board supplies 12V for the transmitter and 5V for the microcontroller and audio circuitry The unit is turned on and off by a digital circuit operated by the left rotary encod...
Page 6: ...thesizer and high precision crystal oscillator The frequency synthesizer uses the high precision oscillator as a reference frequency for the phase detector in the synthesizer The resulting frequency is used to drive the transmitter board The RF TX generator is contained within a shielding fence cover and connection to the transmitter board is made via a RG 174 cable The block diagram in Figure 3 s...
Page 7: ... first stage of the transmitter The signal is amplified through the first stage to drive the gate of the final The RF signal from the second stage is mixed with the microphone audio signal from the main board to drive the final and produce the amplitude modulated signal The resulting signal is then monitored by a diode demodulator to provide a DC signal back to the mainboard to control the power o...
Page 8: ...move the cover assembly see Section 3 1 and verify the unit as being properly powered 2 3 Power Supply Check 1 Check the DC voltage between U119 pin 3 and ground The voltage should be between 4 5 and 5 5V If the voltage is out of limit specified replace the main board 2 Check the DC voltage between L107 and ground The voltage should be between 11 and 13V If the voltage is out of limit specified re...
Page 9: ...p heatsink 3 Remove the top cover by lifting it upwards 3 2 Board and Module Disassembly 3 2 1 Main Board Removal 1 Remove the covers as described in Section 3 1 2 Remove the 2 4 40 x nuts retaining J104 on the rear of the unit 3 Remove the 6 2 56 x panhead screws from the main board 4 De solder the coax cable from J105 5 Carefully slide the main board upward pulling it away from the transmitter b...
Page 10: ...vided to ensure that all AWOS 2000 functions are operating properly 4 1 1 Test Equipment Required A 0 to 30V DC 5 amp power supply AWOS 2000 installation mounting harness Digital multimeter Oscilloscope 20 MHz minimum Radio service monitor IFR 1200S recommended Standard radio headset 4 1 2 Setup Pre set the power supply to 13 75V DC Connect the positive output of the power supply to the red power ...
Page 11: ...rning the flathead screws attached counter clockwise until you hear a click While monitoring with the digital multimeter with the unit transmitting increase R308 to 2V by turning the flathead screws clockwise Verify that the current supplied by the external power supply is less than 2 amps Increase R308 until the output power is 2 5 watts at 118 900 MHz If the voltage from R308 is greater than 4 V...
Page 12: ...CE AND REPAIR MANUAL MAINTENCE AND REPAIR MANUAL MAINTENCE AND REPAIR MANUAL MAINTENCE AND REPAIR MANUAL Revision 1 Page 12 of 13 April 2012 Table 1 Rear Connector Pin Functions PIN TERMINAL FUNCTION 1 GROUND AUDIO RETURN 2 POWER INPUT 13 75 Vdc 3 POWER INPUT 13 75 Vdc 4 TRANSMITTER KEY 5 GROUND 6 GROUND KEY RETURN 7 GROUND 8 No Connection 9 AUDIO IN Figure 5 AWOS 2000 Controls ...
Page 13: ...onics for repair 5 2 Specifications Physical Dimensions Width 5 9 inches Height 2 3 inches Length 7 45 inches Weight 3 0 Lbs Voltage 13 75 0 5 Vdc Current Standby 250 mA Transmit 2 0 A Frequency Range 118 000 to 136 975 MHz Channel Spacing 25 kHz Frequency Stability 001 Spurious Emissions Greater Than 80 dB down from carrier Modulation Adjustable 50 to 90 Typical Temperature Range 35 to 55 Celsius...
