Garmin GTN 725 User manual

190-01007-01 March 2019 Revision 5
GTN 725/750
Maintenance Manual

190-01007-01 GTN 725/750 Maintenance Manual
Rev. 5 Page i
© 2012-2019
Garmin International, Inc. or its subsidiaries
All Rights Reserved
Except as expressly provided herein, 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. Garmin 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®is a registered trademark of Garmin International or its subsidiaries. GTN™ is a trademark of
Garmin International or its subsidiaries. These trademarks may not be used without the express permission
of Garmin.
SD®is a registered trademark of SD-3C, LLC. All rights reserved.
All other products or company names mentioned in this manual are trade names, trademarks, or registered
trademarks of their respective owners.
For aviation product support, visit flyGarmin.com.
For information regarding the Aviation Limited Warranty, refer to Garmin’s website.

190-01007-01 GTN 725/750 Maintenance Manual
Rev. 5 Page ii
RECORD OF REVISIONS
CURRENT REVISION DESCRIPTION
Revision Revision Date Description
103/27/2012 Initial release.
208/21/2014 Document update.
303/22/2016 Added internal datacard removal and replacement procedure.
412/03/2018 Added instructions for installation and removal of HW Mod 7, Battery
Accessory.
503/11/19 Updated internal datacard part number.
Section
Number(s) Page Number(s) Description of Change
5.8 5-10 Updated datacard part number in step 1 of replacement instructions.

190-01007-01 GTN 725/750 Maintenance Manual
Rev. 5 Page iii
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. The information in this document is subject to change without
notice. For updates and supplemental information regarding the operation of Garmin products visit
flyGarmin.com.
GENERAL SAFETY PRECAUTIONS
The following are general safety precautions which are not related to any specific procedure and therefore
do not appear elsewhere in this maintenance manual. These are recommended precautions 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 which 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.

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DEFINITIONS OF WARNINGS, CAUTIONS, AND NOTES
WARNING
This product, its packaging, and its components contain chemicals known to the State of
California to cause cancer, birth defects, or reproductive harm. This Notice is being
provided in accordance with California's Proposition 65. If you have any questions or
would like additional information, please refer to our website at www.garmin.com/prop65.
WARNING
This product contains a Lithium battery which must be recycled or disposed of properly.
Battery replacement and removal must be performed by a Garmin Authorized Repair
Station.
WARNING
Perchlorate Material – special handling may apply.
Refer to www.dtsc.ca.gov/hazardouswaste/perchlorate.
CAUTION
The GTN 725/750 has a display coated with a special anti-reflective coating which is very
sensitive to waxes and abrasive cleaners. CLEANERS CONTAINING AMMONIA WILL
HARM THE ANTI-REFLECTIVE COATING. It is very important to clean the display
using a clean, lint-free cloth and an eyeglass lens cleaner which is safe for anti-reflective
coatings.
WARNING
A warning means injury or death is possible.
CAUTION
A caution means that damage to the equipment is possible.
NOTE
A note provides additional information.

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CAUTION
To avoid damage to the GTN, take precautions to prevent Electro-Static Discharge (ESD)
when handling the GTN, connectors, fan, and associated wiring. ESD damage can be
prevented by touching an object which is of the same electrical potential as the GTN
before handling the GTN itself.
NOTE
All screen shots used in this document are current at the time of publication. Screen shots
are intended to provide visual reference only. All information depicted in screen shots,
including software file names, versions, and part numbers, is subject to change and may
not be up to date.

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GTN 725/750 SERVICE BULLETIN HISTORY
The following table identifies service bulletins for the GTN 725/750. The table is current at the time of
publication of this manual (refer to date on front cover) and is subject to change without notice. Authorized
Garmin Sales and Service Centers are encouraged to access the most up-to-date bulletin and advisory
information on the Garmin Dealer Resource Page at www.garmin.com using their Garmin-provided user
name and password.
Service Bulletin
Number Service Bulletin Date Purpose of Bulletin
1887 12/2018 GTN 6XX/7XX Notification of Mod Level 7
1879 10/26/2018 TSO GTN 6XX/7XX Software Upgrade to Main
Software Version 6.51
1828 09/29/2018 GTN 6XX/7XX TSO Software Upgrade to Main
Software v6.50 and COM Software v2.30
1722 01/26/2018 GTN 6XX/7XX Software Upgrade to Main Software
Version 6.41 and NAV Software Version 6.03
1655 09/19/2016 GTN 6XX/7XX TSO Software Upgrade to Main
Software v6.21 and GMA 35 Version 4.20A/4.21C
1625 06/19/2016 U.S. Forest Service (USFS) and U.S. Department of the
Interior (DOI) Mod Level 6
1581 09/21/2016 GMA 35 Boot Block Software
1580 03/01/2016
GTN 6XX/7XX Software Upgrade to Main Software
Version 6.11 and GMA 35 Audio Software Version
4.10A/4.11C
1559 11/11/2015 GTN 650 750 Notification of Mod Level 5
1526 04/01/2015 GTN 635/650/750 Software Upgrade to COM Software
Version 2.20
1466 01/14/2015 GTN 6XX/7XX Software Upgrade to Main software
Version 5.13 and GMA 35 Audio Software Version 3.10
1406 02/27/2014 GTN 6XX/7XX Software Upgrade to COM Software
Version 2.13
1404 04/03/2014 GTN 650/GTN 750 Notification of Mod Level 4
1369 10/30/2013
GTN 6XX/7XX Software Upgrade Main v4.00, COM
v2.12, GMA 35 Audio v3.05, and Auxiliary Grammar
2.20
1365 12/03/2013 GTN 6XX/7XX Series Unit Installations and ARINC 429
Configuration Settings
1360 10/22/2013
GTN 6XX/7XX Software Upgrade to Main Software
v5.00, COM Software v2.12, and GMA 35 Software
v3.07
1356 10/02/2013 GTN 6XX/7XX Software Upgrade to COM Software
Version 2.12 and GMA 35 ARC Database Version 3.08

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1339 06/19/2013 GTN 625/635/650 and GTN 725/750 TSO Install
Manual Changes - Remove AFMS Section
1321 04/30/2013 TSO Authorization GTN Software Upgrade to Software
V4.10, COM Software V2.11, and GMA 35 V3.05
1319 05/03/2013
GTN 6XX/7XX Software Main 2.00, COM 2.00 or
Service Bulletins 2.01, NAV 6.01, NAV FPGA 1.0,
WAAS 4.00, GMA 35 2.00
1314 05/03/2013 GTN 6XX/7XX Software Version 4.00, COM Software
Version 2.11, and GMA 35 Software Version 3.05
1313 03/25/2013 GTN 625/635/650 and GTN 725/750 Notification
Service Bulletins of Mod Level 3
1311 03/20/2013 GTN 635/650 and GTN 750 Notification of Mod Level 2
1304 05/03/2013 GTN 6XX/7XX Software Upgrade to Software Version
3.01
1236 05/03/2013 GTN 6XX/7XX Software Version 3.00
1216 06/25/2012 GTN 635/650/750 Units and 16W COM Enablement
Card Usage
1203 03/08/2012 GTN 650 and GTN 750 Notification of Mod Level 1
1157 12/02/2011 GTN 6XX/7XX Units and “Data Source” Error Messages
1149 11/11/2011 GTN 6XX/7XX Unit and Synchro Heading Input
1130 10/25/2011 GTN 6XX/7XX Software Upgrade to COM Software
Version 2.01
1128 05/27/2011 GTN 6XX/7XX Unit Installations and RS-232 and
ARINC 429 Configuration Settings
1126 05/11/2011 GTN 7XX/6XX Units with GTS 8XX Traffic Systems
1124 06/16/2011 GTN 650/750 Units and King DME Channeling Issue
1117 04/15/2011 G500 and G600 Installations with GTN 650/750 Units
Service Bulletin
Number Service Bulletin Date Purpose of Bulletin

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TABLE OF CONTENTS
1 GENERAL INFORMATION ................................................................................................................... 1-1
1.1 Scope................................................................................................................................................. 1-1
1.2 Unit Return........................................................................................................................................ 1-1
1.3 Related Publications.......................................................................................................................... 1-1
1.4 Warranty Information ....................................................................................................................... 1-1
1.5 Service Bulletins............................................................................................................................... 1-1
1.6 Technical Specifications................................................................................................................... 1-1
2 GTN 725/750 OVERVIEW .................................................................................................................. 2-1
2.1 Unit Interfaces................................................................................................................................... 2-2
2.2 Control and Operation Information................................................................................................... 2-4
2.3 Periodic Maintenance Instructions.................................................................................................... 2-4
3 THEORY OF OPERATION.................................................................................................................... 3-1
3.1 Front Panel Assembly....................................................................................................................... 3-1
3.2 Main Board ....................................................................................................................................... 3-1
3.3 WAAS Board.................................................................................................................................... 3-1
3.4 I/O Board........................................................................................................................................... 3-1
3.5 COM Board....................................................................................................................................... 3-1
3.6 NAV Board....................................................................................................................................... 3-1
4 TROUBLESHOOTING ........................................................................................................................... 4-1
4.1 LRU Failure Annunciations.............................................................................................................. 4-1
4.2 System Messages .............................................................................................................................. 4-3
5 REMOVAL AND REPLACEMENT PROCEDURES.................................................................................. 5-1
5.1 GTN 725/750 Unit Removal and Replacement................................................................................ 5-2
5.2 GTN Removal with Damaged Jackscrew......................................................................................... 5-3
5.3 Fan Removal and Replacement......................................................................................................... 5-4
5.4 I/O Chassis Removal and Replacement............................................................................................ 5-5
5.5 Memory Battery Removal and Replacement.................................................................................... 5-6
5.6 Bottom Cover Removal and Replacement........................................................................................ 5-8
5.7 Knob Removal and Replacement...................................................................................................... 5-9
5.8 Internal Datacard Removal and Replacement................................................................................. 5-10
6 RETURN TO SERVICE ......................................................................................................................... 6-1
7 SERVICE PARTS LIST ......................................................................................................................... 7-1
APPENDIX A CONNECTOR PINOUT INFORMATION................................................................................ A-1
A.1 J1001 Main Connector - Main Board .............................................................................................. A-2
A.2 J1002 Connector .............................................................................................................................. A-5
A.3 J1003 COM Connector (GTN 750 Only) ........................................................................................ A-6
A.4 J1004 NAV Connector (GTN 750 Only)......................................................................................... A-8
A.5 J1005 I/O Connector...................................................................................................................... A-10
APPENDIX B AFM/AFMS/POH CONSIDERATIONS .............................................................................. B-1

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LIST OF FIGURES
Figure 2-1 GTN 725/750 Control Features ..............................................................................................2-1
Figure 2-2 GTN 725/750 Rear Connectors ..............................................................................................2-2
Figure 2-3 GTN 725/750 Block Diagram ................................................................................................2-3
Figure 4-1 LRU Failure Annunciations ...................................................................................................4-1
Figure 4-2 GTN 725/750 Message Flag ..................................................................................................4-3
Figure 4-3 GTN 725/750 Message Page ..................................................................................................4-3
Figure 5-1 GTN 725/750 Unit Retention Mechanism Adjustment .........................................................5-2
Figure 5-2 Cam Head Removal ...............................................................................................................5-3
Figure 5-3 Fan/Backplate Orientation .....................................................................................................5-4
Figure 5-4 I/O Chassis Removal ..............................................................................................................5-5
Figure 5-5 Memory Battery Location and Orientation ............................................................................5-6
Figure 5-6 Battery Assembly Contacts ....................................................................................................5-7
Figure 5-7 Bottom Cover .........................................................................................................................5-8
Figure 5-8 GTN 725/750 Unit Knobs ......................................................................................................5-9
Figure 5-9 Internal Datacard Access Slot ..............................................................................................5-10
Figure A-1 GTN 725/750 Rear Connectors .............................................................................................A-1

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LIST OF TABLES
Table 1-1 Related Publications ...............................................................................................................1-1
Table 4-1 COM LRU Failure Annunciation Troubleshooting Guide ....................................................4-2
Table 4-2 NAV LRU Failure Annunciation Troubleshooting Guide .....................................................4-2
Table 4-3 GTN 7XX System Messages .................................................................................................4-4
Table 4-4 GPS/SBAS Messages .............................................................................................................4-6
Table 4-5 VLOC/Glideslope Messages (GTN 750 Only) ......................................................................4-7
Table 4-6 COM Messages (GTN 750 Only) ..........................................................................................4-8
Table 4-7 TAWS Messages ....................................................................................................................4-8
Table 4-8 Database Messages ................................................................................................................4-9
Table 4-9 Operational Checks ..............................................................................................................4-10
Table 4-10 Mechanical Failures .............................................................................................................4-11
Table 5-1 Hardware Torque Values .......................................................................................................5-1
Table 7-1 Service Parts ...........................................................................................................................7-1

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1 GENERAL INFORMATION
1.1 Scope
This manual provides general maintenance information for the Garmin GTN 725/750 touchscreen
navigator for use by FAA certified Part 145 repair stations. Repair is limited to LRU-level fault isolation,
replacement, and return to service.
1.2 Unit Return
A Return Merchandise Authorization (RMA) number must be requested from Garmin before a Garmin
unit is returned. Units returned without an RMA will be refused and returned at the sender's expense. Send
units with assigned RMA numbers to the following address:
Garmin International, Inc.
Factory Repair
1200 E. 151st St.
RMA Number: _______
Dock Door #20
Olathe, KS 66062
1.3 Related Publications
The information contained in this manual can be used in conjunction with information from the Garmin
publications listed in this manual, as well as related third party device documentation. The Garmin
publications listed below are available for download from the Garmin Dealer Resource Center.
Table 1-1 Related Publications
1.4 Warranty Information
For complete warranty information, refer to Garmin Aviation Warranty Policies and Procedures
(P/N M02-60069-00) located under the “Policies” tab of the Garmin Dealer Resource Center.
1.5 Service Bulletins
For a complete explanation of Garmin service bulletin policy, refer to Garmin Aviation Warranty Policies
and Procedures (P/N M02-60069-00) located under the “Policies” tab of the Garmin Dealer Resource
Center.
To obtain a list of all Service Bulletins issued for a unit, refer to the Service and Installation Bulletins tab
of the Garmin Dealer Resource Center.
1.6 Technical Specifications
For GTN 725/750 technical specifications, refer to the GTN 725/750 TSO Installation Manual,
(P/N 190-01007-02).
Publication Part Number
GTN 725/750 TSO Installation Manual 190-01007-02
GTN 725/750 Pilot’s Guide 190-01007-03
GTN 725/750 Cockpit Reference Guide 190-01007-04
Garmin Aviation Warranty Policies and Procedures M02-60069-00

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2 GTN 725/750 OVERVIEW
This section describes the function of the GTN 725/750 touchscreen navigator. Periodic maintenance
information is also included. Unless otherwise specified, references made to the “GTN 7XX” will apply
equally to the GTN 725/750.
The GTN 7XX WAAS navigators are a family of panel-mounted GPS/NAV/COM navigators. The GTN
7XX units include the GTN 725 and GTN 750. The GTN 725/750 navigators feature a 6.9" diagonal,
708x600-pixel color LCD touchscreen, shown in figure 2-1. The touchscreen, used to perform most
functions, is supplemented by HOME and DIRECT TO hard keys, as well as audio control and dual
concentric control knobs.
GTN 725
The GTN 725 is a GPS/SBAS unit which may be approved for IFR en route, terminal, non-precision, and
precision approaches. The GTN 725 also has the ability to control the GMA 35 remote audio panel, the
GTX 32/33 remote transponder, and the GDL 88 remote ADS-B transceiver.
GTN 750
In addition to all of the features of the GTN 725, the GTN 750 includes an airborne VHF communications
transceiver and airborne VOR/localizer (LOC) and glideslope (G/S) receivers.
A
UDIO VOLUME KNOB
SD CARD SLOT
TOUCHSCREEN
HOME KE
Y
PHOTOCELL
DIRECT TO KE
Y
CONCENTRIC KNOBS
Figure 2-1 GTN 725/750 Control Features
(GTN 750 Shown)

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2.1 Unit Interfaces
The GTN 725/750 interfaces with other avionics units through the rear connectors shown in figure 2-2.
Figure 2-3 shows a summary of GTN 725/750 external signal and power interfaces. Note that COM and
NAV boards are present only in the GTN 750.
J1001
J1002
J1003
J1004
J1008
J1007
I/O
MAIN
NAV
(GTN 750 only)
COM
(GTN 750 only)
J1006 GPS
J1005
Figure 2-2 GTN 725/750 Rear Connectors
(GTN 750 Shown)
NOTE
COM and NAV boards are not present in the GTN 725. COM and NAV board rear
connector positions on the GTN 725 are covered by blank-out plates.

J1001
POWER & GROUND
MAIN CDI/HSI
(GPS/VOR/ILS)
SWITCHES/
ANNUNCIATORS
EXTERNAL MAP
DISPLAY
CDI/HSI
(VOR/ILS ONLY)
KING SERIAL
TUNED DME
PARALLEL TUNED
DME
ARINC 429
EFIS/EHSI
RMI
AUDIO PANEL
FLIGHT CONTROL
SYSTEM
FUEL/AIR DATA
OR
SERIALIZER
GARMIN
GTN 6XX/7XX
(CROSSFILL)
LIGHTING BUS
TIME MARK OUT
ETHERNET IN
ETHERNET OUT
RS-232 IN
ARINC 429 IN
ARINC 429 OUT
ILS/GPS APPROACH
LAT DEVIATION & FLAGS
TO/FROM
VERT DEVIATION & FLAGS
SUPERFLAGS
MAIN OBS
SWITCHES
ANNUNCIATORS
RS-232 OUT
EXTERNAL INSTRUMENTATION
AIRCRAFT POWER & GROUND
AIRCRAFT LIGHTING BUS
J1002
COM MIC KEY
COM MIC AUDIO
J1003
(GTN 750 only)
J1004
(GTN 750 only)
COM MIC AUDIO
COM REMOTE TRANSFER COM REMOTE TRANSFER SWITCH
COM REMOTE TUNE UP COM REMOTE TUNE
SWITCHES
COM REMOTE TUNE DOWN
MICROPHONE
COM AUDIO
VLOC AUDIO
POWER & GROUND
AIRCRAFT POWER & GROUND
VOR OBI
NAV ARINC 429 IN
NAV ARINC 429 OUT
POWER & GROUND
AIRCRAFT POWER & GROUND
PARALLEL DME TUNING
NAV DME COMMON
NAV REMOTE TRANSFER NAV REMOTE TRANSFER SWITCH
LAT DEVIATION & FLAGS
TO/FROM
VERT DEVIATION & FLAGS
SUPERFLAGS
VOR OBS
VLOC COMPOSITE OUT
NAV ILS ENERGIZE
SERIAL DME CLOCK/DATA
DME REQUEST COMMON
OTHER GARMIN LRUs
ETHERNET IN
ETHERNET OUT
TRAFFIC
ARINC 429 IN
DISCRETES
STORMSCOPE
RS-232 IN
RS-232 OUT
TRANSPONDER
RS-232 IN
RS-232 OUT
ANALOG AUDIO
RS-232 IN
RS-232 OUT
J1005
(GTN 750 ONLY)
RS-232 IN/OUT
ARINC 429 IN/OUT
SYNCRO
J1006
GPS/SBAS ANTENNA
J1007
(GTN 750 ONLY)
COM ANTENNA
J1008
(GTN 750 ONLY)
NAV ANTENNA
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Rev. 5 Page 2-3
Figure 2-3 GTN 725/750 Block Diagram

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Rev. 5 Page 2-4
2.2 Control and Operation Information
GTN 725/750 control and operation information is found in the GTN 725/750 Pilot’s Guide
(P/N 190-01007-03).
2.3 Periodic Maintenance Instructions
2.3.1 Visual Inspection
Periodically inspect the GTN 725/750 display and chassis for corrosion and structural defects. If a defect is
discovered, refer to section 5 for removal and replacement instructions.
2.3.2 Equipment Calibration
No scheduled servicing tasks are required for the GTN 725 or GTN 750.
2.3.3 Cleaning
The GTN 725/750 has a display which is coated with a special anti-reflective coating and is very sensitive
to waxes and abrasive cleaners. CLEANERS CONTAINING AMMONIA WILL HARM THE ANTI-
REFLECTIVE COATING. It is very important to clean the display using a microfiber cloth or with a
clean, lint-free cloth and an eyeglass lens cleaner that is safe for anti-reflective coatings. Care should be
taken to avoid scratching the surface of the display.
The GTN screen can be cleaned during operation by touching the Clean Screen key on the Utilities page.
Press the HOME key to exit Screen Cleaning Mode.
2.3.4 Battery Replacement
WARNING
This product contains a lithium battery which must be recycled or disposed of properly.
Battery replacement and removal must be performed by an Garmin Authorized Repair
Station.
The GTN 725/750 includes an internal lithium battery and will last 5 to 8 years. The battery is used for
internal time clock and GPS system information. Regular, planned replacement is not necessary. The
GTN 725/750 will display “Low Battery” and “Unit Needs Service” messages when replacement is
required. Once the low battery message is displayed, the battery should be replaced within 1 to 2 months. If
the battery is not replaced and becomes totally discharged, the GTN will remain fully operational, but the
GPS signal acquisition time will be increased. There is no loss of function or accuracy of the GTN 725/750
with a dead battery. Refer to section 5.5 for battery removal and replacement instructions and section 6 for
return-to-service information.

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3 THEORY OF OPERATION
3.1 Front Panel Assembly
The front panel assembly of the GTN 725/750 consists of the front panel and the touchscreen. The
GTN 725/750 navigators feature a 6.9" diagonal touchscreen which is used to perform most functions. The
front panel contains a data card slot, photocell, supplemental hard keys, volume control knob, and dual
concentric control knobs.
3.2 Main Board
The GTN 725/750 main board contains the main processor. The GTN 725/750 is capable of interfacing
with other aviation instruments through RS-232, ARINC 429, and Ethernet ports. The GTN 725/750 has a
main indicator function which displays both lateral and vertical deviation from selected course, to/from
indications, lateral and vertical flags and superflags with or without an OBS resolver connection. The
GTN 725/750 also supports configurable discrete inputs and outputs for annunciators, switches, and other
functions.
3.3 WAAS Board
The GTN 725/750 WAAS board contains the functionality of a GPS and Satellite-Based Augmentation
System (SBAS) satellite receiver.
3.4 I/O Board
The I/O board is an expansion board for the main board designed to add functionality to the GTN 750. The
I/O board supports discrete inputs and outputs, additional serial ports, and ARINC transceivers. The I/O
board also supports a synchro interface.
3.5 COM Board
The GTN 750 COM board contains the functionality of a VHF communications transceiver.
3.6 NAV Board
The GTN 750 NAV board contains the functionality of a VOR/LOC receiver and a glideslope receiver.
The GTN 750 NAV board also supports analog and ARINC 429 outputs.

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4 TROUBLESHOOTING
This section contains LRU-level troubleshooting information for the GTN 725/750. Field troubleshooting
tools are organized into two groups:
• LRU failure annunciations
•System messages
Follow the assembly/disassembly procedures in section 5 to remove the GTN unit or component. Follow
instructions in section 1.2 to return the unit or component to Garmin for repair. If the following
troubleshooting approaches are unsuccessful, visit flyGarmin.com.
4.1 LRU Failure Annunciations
Invalid LRU data is indicated by a red X over disabled keys and/or grayed out text at the top of the
touchscreen. Figure 4-1 shows invalid LRU data indications for COM, audio panel, transponder, and
NAV functions.
COM
(GTN 750 Only)
AUDIO PANEL
TRANSPONDER
NAV
(GTN 750 Only)
OPERATION
SQUAWK CODE
AND MODE
Figure 4-1 LRU Failure Annunciations

190-01007-01 GTN 725/750 Maintenance Manual
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Table 4-1 COM LRU Failure Annunciation Troubleshooting Guide
Table 4-2 NAV LRU Failure Annunciation Troubleshooting Guide
(GTN 750 Only)
Cause Isolation Corrective Action
Criterion Corrective Action
Aircraft power to COM
board interrupted.
Check COM circuit
breaker.
COM circuit breaker is
open.
Close COM circuit
breaker.
Disconnect P1003 from
J1003. Inspect
connector assemblies
and pins. Reconnect
P1003 to J1003. Cycle
power on GTN and
check to see if
annunciation is still
present.
J1003 damaged.
Replace the GTN.
Refer to section 5.1 for
details.
Perform a COM
harness power/ground
test. Refer to appendix
A.3 for pinout
information.
COM harness power/
ground circuit
functioning normally.
Replace the GTN.
Refer to section 5.1 for
details.
(GTN 750 only)
Cause Isolation Corrective Action
Criterion Corrective Action
Aircraft Power to NAV
board interrupted.
Check NAV circuit
breaker.
NAV circuit breaker is
open.
Close NAV circuit
breaker.
Disconnect P1004 from
J1004. Inspect
connector assemblies
and pins. Reconnect
P1004 to J1004. Cycle
power on GTN and
check to see if
annunciation is still
present.
J1004 damaged.
Replace the GTN.
Refer to section 5.1 for
details.
Perform a NAV harness
power/ground test.
Refer to appendix A.4
for pinout information.
NAV harness power/
ground circuit
functioning normally.
Replace the GTN.
Refer to section 5.1 for
details.

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4.2 System Messages
GTN 725/750 System messages are accessed by touching the MSG key on the Home page, shown in
figure 4-2. System messages are also displayed on the Message page, shown in figure 4-3.
Figure 4-2 GTN 725/750 Message Flag
Figure 4-3 GTN 725/750 Message Page