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Old 03-18-2018, 09:20 PM
mwardle7 mwardle7 is offline
Join Date: Oct 2009
Location: Utah
Posts: 62
Smile G3X GPS Data Out to ACK E-04 Hints for RV-12

I just went through a troubleshooting exercise to ensure that the GPS data from my G3X is being properly transmitted to the ACK E-04 ELT. This is important because without the GPS data being sent to the ELT, the ELT cannot send GPS position data on the 406 Mhz frequency. In case of an accident, I want search and rescue services to have all the data I can give them.

Below are a few lessons learned that I hope will be helpful to someone else in the future. In order for these notes to make sense, you'll need to carefully review the ACK E-04 ELT Manual and the Garmin G3X Touch Installation Manual RS-232 Settings. As of the date of this post, I found the ACK E-04 Manual to be lacking in providing the necessary configuration settings for the G3X, so use caution when interpolating information from the manual on Garmin settings. The information below will hopefully bridge the gap of missing info in the ACK Manual.

Here we go:

1. GPS Test Tool. Figure 14 in the ACK E-04 ELT Manual shows how to make a test tool to determine if the GPS data is being received at the ELT. Study Figure 14 carefully. You'll note that the LED diode has a short lead and a long lead. LEDs should come with one lead shorter than the other. Attach the 300 ohm 1/4 watt resister to the short lead, not the long lead.

I attached a spade connector to the positive lead on my GPS Test Tool and on the wire coming out of PIN 2 of the ELT RS-232 DIN connector, which made connecting/disconnecting the test tool very easy.

2. DIN Connector. I didn't like the RS-232 DIN Cable coming out of the ELT control module. I replaced it with a 4-pin Molex connector. Testing continuity on both ends of each pin on the RS-232 DIN connector enabled me to determine which of the four wires in the telephone cable were associated with PINs on the RS-232 connector.

3. G3X Settings for ELT Data. The ELT allows serial data to be transferred from the G3X to the ELT at various baud rates. The default baud rate on the ELT from the factory is 9600. Other baud rates require jumping pins on the ELT control module. In earlier versions of the G3X software, the 9600 baud rate was not available when the serial port was set to NMEA Out; 4800 was the only available baud rate, which would require jumping pins on the ELT control board. I believe the RV-12 G3X Configuration File was set to 4800 Baud when I installed my system, and I suspect that is the case for the current version of the configuration file. So, if I am correct, the default configuration for the RV-12 G3X software is not plug and play for the default setting on the E-04 ELT. Ugh.

In a later software release, the G3X Touch hardware configuration added the ability to output serial data formatted as NMEA Out at 9600 Baud. I think it is easier to change the software setting to 9600 Baud than to jump pins on the ELT. Rather than messing with the ELT control module, I would suggest that you simply change the settings on the G3X. Here's how you do that:

A. Start the G3X in configuration mode by holding down the Menu key when you turn on the master switch.
B. Navigate to the RS-232 configuration page.
C. The ELT GPS Data is on the RV-12 wiring harness is transmitted on Serial Port #4. Make sure Serial Port #4 is configured to NMEA Out at 9600 Baud.
D. Click the button "Configure NMEA Output." Set the Output Rate to Normal, not fast. Normal allows the data to follow the GPGGA format, which is the format used by the E-04. Select the Lat/Lon format with the most letters (DDMM.MMMM). You'll note that the data format in the ACK E-04 Manual doesn't match the formats offered by the G3X; this doesn't matter because you can pick any of the formats offered by the G3X and the ACK ELT will read the data. By selecting the Lat/Lon format with the greatest number of letters, you'll pick the data format with the highest resolution, and thus transmit the most accurate GPS location.

4. GPS Data Wire Grounding Issues. If you are unsuccessful at getting the GPS Test LED tool to blink showing that proper data is being sent, you may have a grounding problem. Test continuity from PIN 4 of the ELT RS-232 DIN Connector to ground, and also test continuity to ground from PIN 40 on the EIFS Harness that plugs into the the back of the G3X Touch. If you have continuity to ground, then you won't get the LED GPS Data test tool to work.

There are two places where you might have a ground fault:

A. Shielding Issue on PIN 4 on the RS-232 Din Connector. When you solder the ELT wires from the Fuselage Harness to the tiny pins on the RS-232 Connector it is easy to neglect to observe that the WH-F395 GPS Data Out Wire is shielded. The shielding is wired to ground in the Fuselage harness where it plugs in to the AV-5000 Module. So, if you don't strip back the shielding and isolate it from PIN 4 on the ELT Din Harness, you will short the GPS data wire to ground and the data won't transmit properly. This can be remedied by stripping back the shielding about an inch, trimming of the shielding without damaging the inner wire insulation, and covering the remaining exposed shielding with heat shrink.

B. Grounding Issue in the AV-5000 Module. There is a known issue that some AV-5000 Module boxes have a grounding problem relating to the GPS Data wire. See the RV-12 Service Notification dated September 10, 2014, Notification 14-09-10 ( The best way to see if you have the problem referenced in this service bulletin is to remove the EFIS and Fuselage serial connectors from the AV-5000 Module, create a jumper wire from PIN 21 on the Fuselage connector and PIN 10 on the EFIS connector on the AV-5000 Module, and check continuity to ground from the jumper wire. If you have continuity to ground, your problem is in the AV-5000 Module, and you'll need to complete the work as described in the Service Notification.

I hope this information is helpful to all.

Obligatory disclaimer: The Vans manuals, Garmin Manuals, and ACK manuals trump here. If you are not well versed in electrical systems, get help from a professional. If you let the proverbial smoking genie out of your electrical system - it's your fault.
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