Garmin GTX 327 ATC User manual

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GARMIN International, Inc.
1200 E. 151st Street
Olathe, KS 66062 USA
190-00187-05 Revision B
December 2001
GTX327ATC
TRANSPONDER
MAINTENANCE
MANUAL
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Page A GTX 327 MAINTENANCE MANUAL
Rev. B 190-00187-05
© Copyright 2000-2001
GARMIN Corporation
All Rights Reserved
Except as expressly provided below, no part of this manual may be reproduced, copied, transmitted,
disseminated, downloaded or stored in any storage medium, for any purpose without the express prior
written consent of GARMIN Corporation. GARMIN Corporation hereby grants permission to download a
single copy of this manual and of any revision to this manual onto a hard drive or other electronic storage
medium to be viewed and to print one copy of this manual or of any revision hereto, provided that such
electronic or printed copy of this manual or revision must contain the complete text of this copyright notice
and provided further that any unauthorized commercial distribution of this manual or any revision hereto is
strictly prohibited. GARMIN International, Inc.
1200 E. 151st Street
Olathe, KS 66062 USA
Telephone: [phone]
Dealer Line: 1-800-800-1420
Website Address: www.garmin.com
INFORMATION SUBJECT TO EXPORT CONTROL LAWS
This document may contain information which is subject to the Export Administration
Regulations ("EAR") issued by the United States Department of Commerce (15 CFR, Chapter
VII, Subchapter C) and which may not be exported, released, or disclosed to foreign nationals
inside or outside of the United States without first obtaining an export license. A violation of the
EAR may be subject to a penalty of up to 10 years imprisonment and a fine of up to $1,000,000
under Section 2410 of the Export Administration Act of 1979. Include this notice with any
reproduced portion of this document.
RECORD OF REVISIONS
Revision Revision
Date Description ECO #
A11/17/00 Initial Release ----
B12/3/01 Added MTL level 16794
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GTX 327 MAINTENANCE MANUAL Page i
190-00187-05 Rev. B
GENERAL MAINTENANCE PRECAUTIONS
The following are general safety precautions that are not related to any specific procedure and therefore do not
appear elsewhere in this maintenance manual. These are recommended precautions that personnel should
understand and apply during the many phases of maintenance and repair.
KEEP AWAY FROM LIVE CIRCUITS. Maintenance personnel shall observe all safety regulations at all
times. Do not replace components inside the equipment when potentially lethal voltages are present. Turn off
system power before making or breaking electrical connections. Regard any exposed connector, terminal
board, or circuit board as a possible shock hazard. Components that retain a charge shall be discharged only
when such grounding does not result in equipment damage. If a test connection to energized equipment is
required, make the test equipment ground connection before probing the voltage or signal to be tested.
DO NOT SERVICE ALONE. Personnel shall not under any circumstances reach into or enter any enclosure
for the purpose of servicing or adjusting the equipment without immediate presence or assistance of another
person capable of rendering aid.
NOTE
Specialized test equipment and extensive depot level repair training are required for testing the equipment
covered in this manual. Therefore, this manual may not be used to test or repair the subject equipment unless
the using facility has been specifically authorized by GARMIN to do so.
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GTX 327 MAINTENANCE MANUAL
Rev. B 190-00187-05
Page ii
TABLE OF CONTENTS
SECTION 1
DESCRIPTION AND OPERATION
PARAGRAPH PAGE
1.1 INTRODUCTION............................................................................................................ 1-1
1.2 GENERAL DESCRIPTION............................................................................................. 1-1
1.3 PURPOSE OF EQUIPMENT.......................................................................................... 1-2
1.3.1 ATCRBS System Operation ..................................................................................... 1-2
1.3.2 Interrogator...............................................................................................................1-3
1.3.3 Transponder............................................................................................................. 1-3
1.3.4 Radar Screen, TCAS Display ................................................................................... 1-4
1.3.5 Mutual Suppression Pulses ...................................................................................... 1-4
1.4 TECHNICAL SPECIFICATIONS .................................................................................... 1-4
1.5 SCOPE OF MAINTENANCE.......................................................................................... 1-5
1.6 EQUIPMENT DESCRIPTION......................................................................................... 1-5
1.6.1 Main Board Assembly............................................................................................... 1-6
1.6.2 Front Panel............................................................................................................... 1-6
1.6.3 Transmitter............................................................................................................... 1-6
1.6.4 Receiver...................................................................................................................1-6
1.6.5 Diplexer Coax Cable................................................................................................. 1-7
1.6.6 Flexible Circuit Cables.............................................................................................. 1-7
SECTION 2
SPECIAL TEST EQUIPMENT
2.1 INTRODUCTION............................................................................................................ 2-1
2.2 SPECIAL TOOLS AND TEST EQUIPMENT .................................................................. 2-1
2.2.1 Antenna Test Cable Connector................................................................................. 2-1
2.2.2 Test Harness............................................................................................................ 2-2
2.2.3 Transponder Bench Test.......................................................................................... 2-2
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GTX 327 MAINTENANCE MANUAL Page iii
190-00187-05 Rev. B
SECTION 3
TROUBLESHOOTING
3.1 TROUBLESHOOTING EQUIPMENT ............................................................................. 3-1
3.2 TROUBLESHOOTING THE GTX 327............................................................................ 3-1
3.3 INITIAL INSPECTION OF UNIT..................................................................................... 3-2
3.4 FUNCTIONAL TEST, STANDARD TEST SETUP AND TEST SIGNAL.......................... 3-2
3.5 POWER ON CHECK...................................................................................................... 3-2
3.6 MAIN BOARD ASSEMBLY............................................................................................. 3-3
3.7 DISPLAY ASSEMBLY.................................................................................................... 3-3
3.8 RECEIVER AND TRANSMITTER ASSEMBLIES........................................................... 3-5
SECTION 4
DISASSEMBLY AND REASSEMBLY
4.1 INTRODUCTION............................................................................................................ 4-1
4.2 REQUIRED TOOLS....................................................................................................... 4-1
4.3 DISASSEMBLING THE UNIT......................................................................................... 4-1
4.3.1 Removing the Bottom Cover..................................................................................... 4-2
4.3.2 Flexible Circuit Cables.............................................................................................. 4-2
4.3.3 Front Panel Assembly............................................................................................... 4-2
4.3.4 Display Assembly ..................................................................................................... 4-3
4.3.5 Receiver Module Assembly ...................................................................................... 4-3
4.3.6 Transmitter Board..................................................................................................... 4-3
4.3.7 Main Board............................................................................................................... 4-4
4.3.8 Coaxial Cable Diplexer Assy..................................................................................... 4-4
4.4 REASSEMBLY............................................................................................................... 4-5
4.4.1 Coaxial Cable Diplexer Assy..................................................................................... 4-5
4.4.2 Main Board............................................................................................................... 4-5
4.4.3 Transmitter Board..................................................................................................... 4-6
4.4.4 Receiver Module Assembly ...................................................................................... 4-6
4.4.5 Display Assembly ..................................................................................................... 4-7
4.4.6 Front Panel Assembly............................................................................................... 4-7
4.4.7 Flexible Circuit Cables.............................................................................................. 4-7
4.4.8 Installing Bottom Cover............................................................................................. 4-8
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GTX 327 MAINTENANCE MANUAL
Rev. B 190-00187-05
Page iv
SECTION 5
TESTING
5.1 INTRODUCTION............................................................................................................ 5-1
5.2 GENERAL......................................................................................................................5-1
5.3 ADJUSTMENT/MEASUREMENT ACCURACY.............................................................. 5-1
5.4 TEST EQUIPMENT PRECAUTION................................................................................ 5-2
5.5 REQUIRED TEST EQUIPMENT .................................................................................... 5-2
5.5.1 TEST HARNESS...................................................................................................... 5-2
5.6 BENCH TESTING.......................................................................................................... 5-2
5.7 TEST EQUIPMENT SETUP........................................................................................... 5-2
5.7.1 ATC-1400A and Oscilloscope Default Settings......................................................... 5-4
5.8 STANDARD TEST SIGNALS......................................................................................... 5-4
5.8.1 Input Voltages .......................................................................................................... 5-4
5.8.2 RF I/O....................................................................................................................... 5-4
5.9 POWER ON CHECK...................................................................................................... 5-4
5.9.1 28 V Panel Lighting .................................................................................................. 5-5
5.9.2 14 V Panel Lighting .................................................................................................. 5-5
5.9.3 5 V Panel Lighting .................................................................................................... 5-5
5.9.4 Power On Test ......................................................................................................... 5-5
5.9.5 Display Dimming Test............................................................................................... 5-6
5.10 SWITCHED POWER OUTPUT...................................................................................... 5-6
5.11 FRONT PANEL PUSHBUTTON CONTROLS................................................................ 5-6
5.11.1 Timer Function Test.................................................................................................. 5-7
5.11.2 Code Selector Pushbutton Switches......................................................................... 5-7
5.11.3 Configuration Pages................................................................................................. 5-7
5.12 FUNCTIONAL TEST...................................................................................................... 5-7
5.12.1 Receiver Test, Minimum Trigger Level and Dynamic Range .................................... 5-8
5.12.2 Transmitter Power Output and Reply Annunciator Test............................................ 5-8
5.12.3 Transmitter Characteristics....................................................................................... 5-8
5.12.4 Reply Rate Limiting Test......................................................................................... 5-10
5.12.5 Side Lobe Suppression........................................................................................... 5-10
5.12.6 IDENT Test............................................................................................................. 5-11
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GTX 327 MAINTENANCE MANUAL Page v
190-00187-05 Rev. B
SECTION 6
REPLACEABLE ASSEMBLIES
6.1 LIST OF REPLACEABLE PARTS.................................................................................. 6-1
SECTION 7
ASSEMBLY DRAWINGS
7.1 ASSEMBLY DRAWINGS ............................................................................................... 7-1
LIST OF FIGURES
Figure Page
1-1 ATCRBS System .......................................................................................................... 1-2
1-2 Typical TCAS Encounter............................................................................................... 1-3
1-3 GTX 327 System Block Diagram .................................................................................. 1-5
2-1 Blindmate Antenna Connector...................................................................................... 2-1
2-2 DB-25 Pin-Out Definitions............................................................................................. 2-3
2-3 GTX 327 Test Setup/Test Harness............................................................................... 2-5
3-1 4 kHz PWM Signal on Q501......................................................................................... 3-4
3-2 Main Board Component Layout..................................................................................... 3-8
3-3 Transmitter Board Component Layout.......................................................................... 3-9
3-4 Receiver Board Component Layout............................................................................ 3-10
4-1 Diplexer Cable Orientation............................................................................................ 4-5
5-1 ATC-1400A Test Set..................................................................................................... 5-3
5-2 Transmitter Shield Cover Alignment Cutouts .............................................................. 5-10
7-1 GTX 327 Front Panel Assembly.................................................................................... 7-1
7-2 GTX 327 Chassis Assembly, Exploded View................................................................ 7-3
7-3 GTX 327 Chassis Assembly, Main Board and Transmitter Board................................. 7-5
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GTX 327 MAINTENANCE MANUAL Page 1-1
190-00187-05 Rev. B
SECTION 1
DESCRIPTION AND OPERATION
1.1 INTRODUCTION
This manual provides functional testing and assembly level maintenance information for the GARMIN GTX 327
Digital Display Transponder System. Information pertaining to the installation and operating instructions can be
found in the GTX 327 Installation Manual, 190-00187-02. This manual is designed to aid the bench technician in
isolating failures to the assembly level only. If necessary, the GTX 327 can be returned to GARMIN for all
service work, including maintenance and repair. Contact GARMIN at the following address for more details:
GARMIN
1200 E. 151st Street
Olathe, KS 66062
Telephone: [phone]
Dealer Line: 1-800-800-1420
Website Address: www.garmin.com
1.2 GENERAL DESCRIPTION
The GARMIN GTX 327 is a panel-mounted TSO’d transponder with the addition of timing functions. The
transponder is a radio transmitter and receiver that operates on radar frequencies, receiving ground radar
interrogations at 1030 MHz and transmitting a coded response of pulses to ground-based radar on a frequency of
1090 MHz.
As with other Mode A/Mode C transponders, the GTX 327 replies with any one of 4,096 codes, which differ in
the position and number of pulses transmitted. By replying to ground transmissions, the GTX 327 enables ATC
to display aircraft position, identification, encoded altitude and groundspeed on ATC radar screens. The
GTX 327 is equipped with IDENT capability (IDENT key) that activates the Special Position Identification (SPI)
pulse for 18 seconds.
The GTX 327 is configured with all pushbutton key controls. The layout of the front panel keys and displays
segregates the transponder’s primary functions from the secondary timing functions. The unit can be configured
so the aircraft avionics master bus can turn the unit on.
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1-2 GTX 327 MAINTENANCE MANUAL
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1.3 PURPOSE OF EQUIPMENT
The GARMIN GTX 327 Transponder System provides an air to ground link in the Air Traffic Control Radar
Beacon System (ATCRBS) to support in-flight aircraft identification. It also provides air to air link participation
in the airborne Traffic Alert and Collision Avoidance System (TCAS) for aircraft equipped with Traffic
Avoidance equipment.
A pulsed interrogation from the ground-based secondary radar or airborne TCAS generates a pulsed reply from
the GTX 327. These pulses are processed and displayed on an ATC radar screen on the ground or traffic display
in other aircraft. Normal radar returns from the primary radar system would vary in intensity depending on
aircraft size, distance away and other factors. The Transponder System equalizes returns by providing similar
digital data for all aircraft.
Selected codes enable the GTX 327 to reply with identification information useful to ATC. Special codes may
be selected to indicate conditions such as emergency or VFR traffic.
In addition to Mode A operation for identification, Mode C is available for altitude information when an altitude
encoder is connected to the GTX 327 and altitude replies are selected.
1.3.1 ATCRBS System Operation
There are two classes of radar systems used by ATC, primary and secondary. Primary class includes surveillance
or search radar. The secondary class is comprised of special purpose radar including ATC interrogators and
transponders. Secondary radar is able to obtain data that cannot be determined by primary radar alone. The
secondary radar is officially referred to as the Air Traffic Control Radar Beacon System or ATCRBS. The
essential elements of the ATCRBS are show in figure 1-1.
Figure 1-1. ATCRBS System
REPLIES
INTERROGATION 1030 MHZ
REPLY 1090 MHZ
INTERROGATION ANTENNA
SECONDARY RADAR
PRIMARY RADAR
A
NTENN
A
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GTX 327 MAINTENANCE MANUAL Page 1-3
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1.3.2 Interrogator
The ATC ground based interrogator rotates synchronously with the primary surveillance radar and transmits a
sequence of pulses at a frequency of 1030 MHz. The interrogation repeatedly requests all transponders on the
mode being used to reply. The received replies are available for display on the ATC radar screen.
There are five types of interrogation modes, A, B, C, D and S which may be transmitted by the ground station.
Each interrogation mode is distinct from the other and is characterized by the spacing of the transmitted framing
pulses. The GARMIN GTX 327 is designed for Mode A and Mode C operation.
Similar to the ground based interrogator, an airborne TCAS processor transmits interrogation signals searching
for airborne traffic in relatively close proximity. TCAS is capable of detecting the direction and altitude of an
aircraft equipped with a transponder such as the GARMIN GTX 327. Typical TCAS equipment is shown in
figure 1-2.
Figure 1-2. Typical TCAS Encounter
1.3.3 Transponder
When the interrogation signal is detected by the GTX 327, an appropriate response is generated. This response is
transmitted omnidirectionally by the GTX 327 at a frequency of 1090 MHz. When multiple replies return to the
interrogating system, appropriate equipment processes the identification, altitude, distance and azimuth data to
compute location, speed and direction information for appropriate use.
INTERROGATION AND REPLY
SIGNALS
TCAS DISPLAY
TCAS EQUIPPED AIRCRAFT
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1.3.4 Radar Screen, TCAS Display
The radar screen displays returns from both the primary surveillance radar system and the ATCRBS. The ATC
system controllers use these returns, called targets, to identify traffic. Similarly, the TCAS display indicates the
presence of airborne traffic showing direction, distance and altitude.
1.3.5 Mutual Suppression Pulses
Other equipment on board the aircraft may transmit in the same frequency band as the transponder, such as DME
or another transponder. Mutual suppression is a synchronous pulse that is sent to the other equipment to suppress
transmission of a competing transmitter for the duration of the pulse train transmission. The transponder
transmission may be suppressed by an external source and other equipment on board may be suppressed by the
transponder. This feature is designed to limit mutual interference.
1.4 TECHNICAL SPECIFICATIONS
Refer to the GTX 327 Installation Manual for a complete list of specifications.
SPECIFICATION CHARACTERISTIC
TSO, JTSO TSO C74c Class 1A, JTSO-C74c Class 1A
RTCA/DO-160D Refer to GTX 327 Installation and Operation Manual,
190-00187-02, Appendix A
Power Requirements 11.0 to 33.0 Vdc; Power Input: 15 Watts typical, 22 Watts
maximum
Transmitter Frequency 1090 MHz
Transmitter Power 125 Watts minimum, 150 Watts nominal at the antenna
through 1.5 dB coax.
Receiver Frequency 1030 MHz
Receiver Sensitivity -74 dBm Nominal for 90% replies*
Mode A Capability 4096 Identification Codes
Mode C Capability 100 Foot Increments from –1000 to 63,000 feet
External Suppression Input Low ≤0.5 V; High ≥8 V
* Units P/N 011-00490-00 prior to S/N 83707331, P/N 011-00490-01 prior to S/N 83925021 and
P/N 011-00490-10 prior to S/N 84000116 have an MTL of -72 dBm.
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GTX 327 MAINTENANCE MANUAL Page 1-5
190-00187-05 Rev. B
1.5 SCOPE OF MAINTENANCE
GARMIN recommends limiting field maintenance to the following:
•Functional inspection to meet current FAR requirements
•Functional testing to the board level
•Replacement of major subassemblies
•Replacement of Flexible Circuit Cables
1.6 EQUIPMENT DESCRIPTION
The GTX 327 consists of four major electrical assemblies:
•Main Board Assembly
•Receiver Board
•Transmitter Board
•Front Panel Subassembly
Refer to figure 1-3 for a simplified system block diagram. The subassemblies are not field repairable. For a
complete list of all GARMIN authorized replaceable parts, see Table 6-1, Field Replaceable Parts List.
DIPLEXER MAIN BOARD LCD DISPLAY
AND
KEYBOARD
TRANSMITTER
MODULATOR
RECEIVER
Figure 1-3. GTX 327 Simplified System Block Diagram
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1-6 GTX 327 MAINTENANCE MANUAL
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1.6.1 Main Board Assembly
The Main Board Assembly is the functional center of the unit. The Main Board communicates with all the
components of the unit, and provides information to and from the Front Panel for the interface with the pilot.
The Main Board contains the following circuits:
•Power Supply
•Programmable Logic Device, EE PROM, microprocessor with flash and SRAM memory.
•Decoder/Encoder
•Light Dimming Circuit
•Switched Power Output
•I/O Filters
•RS-232 Circuitry
1.6.2 Front Panel
The Front Panel Subassembly provides the pilot/transponder interface. The Front Panel displays the timing and
transponder functions and enters the selected code, SPI and timing commands. The Front Panel contains the
following circuits:
•LCD Display with LED backlighting
•Mode Selection Keys
•Pushbutton Data Entry Keys
•Ambient Light Sensor
1.6.3 Transmitter
The Transmitter transmits the coded pulses. The Transmitter contains the following circuits:
•Pulse Modulator
•Ceramic Resonator with Pulse Power Oscillator
•Power Amplifier
•Low Pass Filter
1.6.4 Receiver
The Receiver receives the interrogation signals. The Receiver contains the following circuits:
•970 MHz Local Oscillator
•1030 MHz Bandpass filter
•60 MHz I.F.
•Mixer
•Detector
•Receiver Voltage Regulator
•Log Amplifier, Video Amplifier
•Rate Limiter
•Pulse Processing circuits
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GTX 327 MAINTENANCE MANUAL Page 1-7
190-00187-05 Rev. B
1.6.5 Diplexer Coax Cable
The GTX 327 Receiver and Transmitter are connected to a common BNC connector at the rear of the unit
through subminiature coax cables and RF connectors.
Cable length and placement of this cable is critical to proper operation. The cable assy is used as a diplexer,
allowing both the transmitter and receiver to use the same BNC antenna connector. The transmitter and receiver
operate 60 MHz apart (TX at 1090 MHz and RCV at 1030 MHz). At 1090 MHz the coax cable going to the
receiver appears as an open circuit while at 1030 MHz, the coax cable going to the transmitter appears as an open
circuit.
The routing of the coax cables inside the unit is critical as well.
Note how the cables are routed before removing. Make sure the cables are replaced in the same location as
originally installed.
1.6.6 Flexible Circuit Cables
The major subassemblies are interconnected by means of ZIF (Zero Insertion Force) flexible circuit cables and
one ribbon cable. These cables are readily available for replacement in case of damage.
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1-8 GTX 327 MAINTENANCE MANUAL
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GTX 327 MAINTENANCE MANUAL Page 2-1
190-00187-05 Rev B
SECTION 2
SPECIAL TEST EQUIPMENT
2.1 INTRODUCTION
This section identifies the special test equipment essential to maintain the GTX 327. Standard equipment is not
listed. For any questions regarding warranty repair of the unit contact the GARMIN Customer Service
Department at the address or phone number listed in Section 1.
2.2 SPECIAL TOOLS AND TEST EQUIPMENT
•ATC-1400A Transponder Test Set or equivalent
•Power Supply
•Oscilloscope
•Digital Voltmeter
•50 8Antenna Test Cable Connector—Locally Fabricated
•Test Harness—Locally Fabricated (See figure 2-3)
•Coaxial Adapter: Female BNC to male type N
2.2.1 Antenna Test Cable Connector
The antenna test cable requires a BNC connector at the test fixture antenna and a male BNC “Blindmate”
connector (GARMIN P/N 330-00198-00) or RF Adapter (P/N 330-00326-00) at the GTX 327 Transponder.
Instructions for installing the Blindmate BNC are shown in steps 1 through 7 and illustrated in Figure 2-1.
Follow BNC connector manufacturer instructions for assembly of the BNC connector. The RF attenuation at
1090 MHz of the cable must not exceed 1.50 dB.
Figure 2-1. Blindmate Antenna Connector
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2-2 GTX 327 MAINTENANCE MANUAL
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1. Trim coax outer insulation back 0.50”.
2. Trim braid (not center conductor or insulation) back 0.25”.
3. Strip Insulation back 0.12”.
NOTE
Place the ferrule over the coax braid, flush against the coax outer insulation
before performing the next step if the outside diameter of the coax braid is
smaller than the inside diameter of the center connector sidewall opening.
4. Insert cable (center conductor, dielectric and shield braid) through the sidewall of the connector
and solder the center conductor to the center pin of the connector.
NOTE
When using low loss cable it may be necessary to flatten the solid wire center
conductor slightly so it can fit the slot on the RF connector center pin. When
soldering, avoid applying excess heat to the connector body, and center
conductor insulator.
5. Heat the outside of the connector sleeve and at the same time apply solder between the braid and
the sleeve. Continue to apply heat until the solder flows evenly.
6. Install 50 8Matching Bushing.
7. Insert connector cap and tack solder in two places.
2.2.2 Test Harness
A test harness must be fabricated locally to connect the GTX 327 to the ATC-1400A Transponder Test Set. All
electrical connections, except for the antenna, are made through a single, 25 pin D connector. Figure 2-2 defines
the electrical characteristics of all input and output signals and identifies the cable requirements for each signal.
Connector orientation in the figure is viewed from the rear of the unit. Refer to Figure 2-3 when fabricating the
test harness.
2.2.3 Transponder Bench Test
The Transponder Bench Test verifies the GTX 327 basic operation:
•Reply codes for modes A and C
•Transmitter Frequency and Power
•Minimum Trigger Level (MTL)
•Side Lobe Suppression
•Receiver Dynamic Range
•Backlighting
•Switched Power Output
•Remote Inputs (As listed in the test harness diagram)
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GTX 327 MAINTENANCE MANUAL Page 2-3
190-00187-05 Rev B
Unit Connector As Viewed From Rear Of Unit.
PIN DESCRIPTION I/O
1 AVIONICS MASTER ON In
2 RS232 IN 2 In
3 ALTITUDE A1 In
4 ALTITUDE C2 In
5 ALTITUDE A2 In
6 ALTITUDE A4 In
7 ALTITUDE C4 In
8 EXTERNAL IDENT INPUT In
9 ALTITUDE B1 In
10 ALTITUDE C1 In
11 ALTITUDE B2 In
12 ALTITUDE B4 In
13 POWER GROUND In
14 SWITCHED POWER OUTPUT Out
15 POWER INPUT (+11 TO +33 VDC) In
16 EXTERNAL STANDBY In
17 EXTERNAL SUPPRESSION In/Out
18 ALTITUDE D4 In
19 RS232 IN 1 In
20 RS232 OUT 1 Out
21 RESERVED --
22 SQUAT SWITCH In
23 28 VDC PANEL LIGHTING INPUT In
24 14 VDC/5 VDC PANEL LIGHTING INPUT In
25 POWER GROUND In
Figure 2-2. DB-25 Pin-Out Definitions
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2-4 GTX 327 MAINTENANCE MANUAL
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