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  #1  
Old 07-05-2016, 01:58 PM
Brantel's Avatar
Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,513
Default The rest of the story....




A couple weeks ago I started a thread related to the GA35 antenna and what looked like the second failure of the same on my airplane.

Due to my history with a prior GA35 antenna failure and the fact that mine had ran for 4 years under the cowl of my RV7, I incorrectly assumed that the heat had finally killed my second antenna.

I have to tell you that this was a wrong assumption worth just north of $300!

Turns out after installing a third new GA35 antenna, new coax cable and connectors, and even trying a forth WAAS enabled antenna of a different brand/model, it was determined that there was absolutely nothing wrong with the second antenna that I totally destroyed just to see how it was made inside....

The rest of the story is that the root cause ended up being within the GTN650 itself. The symptoms were that once the unit heated up to operating temp, the main board would lose communication with the GPS board resulting in an indication of loss of sat lock/signal. The cooler the ambient temp, the longer it would take. The warmer the ambient temp, the faster this would happen. Many times this would happen in a cyclical fashion depending on the ambient temp. Once the unit got warm enough, it would just fail completely.

Anyway, Trek Lawler and the rest of the team back at Garmin did an awesome job supporting me in my effort to find the root cause of the issues with my GPS. Once a repeatable failure mode was identified, the unit went back to Garmin and arrived there on Friday and I had it back in my hands on the following Thursday! Super fast service! The tech's confirmed a failed/failing GPS board.

The GTN has been performing flawlessly on the flights since repair.

Thank you Trek, TeamX and Garmin for amazing support even after the warranty period has expired!
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Brantel (Brian Chesteen),
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RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
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Last edited by Brantel : 07-05-2016 at 08:32 PM.
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  #2  
Old 07-05-2016, 03:16 PM
bkthomps bkthomps is offline
 
Join Date: Jan 2010
Location: Destin
Posts: 1,546
Default

interesting, very interesting...my brand new GTN units behaved this way, and the twist was- the antennas were the previously installed ones used on my 530/430, same location, same antenna, same wiring

but i'd get signal drop outs, on the 750 and 650, it hasn't happened recently that i can recall, but i haven't changed anything either.....curious if this is seasonal or temperature related, i'll pay closer attention now
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  #3  
Old 07-05-2016, 03:35 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,322
Default Good News

WOW, Brian - - it is really good to hear that the GA35 is not still failure prone, that temps are in line for the under-cowl location, that we now know what installation issues were leading to the failures, and that you won't be buying anymore GA35's any time soon.


Also, not least, that the Garmin Team upheld their well earned reputation for support. Your 650 unit was not that old either!?!? Right?

Back flying with a happy pilot and panel. - - - priceless
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  #4  
Old 07-05-2016, 07:25 PM
Brantel's Avatar
Brantel Brantel is offline
 
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Location: Newport, TN
Posts: 7,513
Default

Quote:
Originally Posted by bkthomps View Post
interesting, very interesting...my brand new GTN units behaved this way, and the twist was- the antennas were the previously installed ones used on my 530/430, same location, same antenna, same wiring

but i'd get signal drop outs, on the 750 and 650, it hasn't happened recently that i can recall, but i haven't changed anything either.....curious if this is seasonal or temperature related, i'll pay closer attention now
Brian,

When I get a chance, I will post some images on how to help diagnose for this issue. Stay tuned to this thread....
__________________
Brantel (Brian Chesteen),
Check out my RV-10 builder's BLOG
RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook
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  #5  
Old 07-05-2016, 07:27 PM
Brantel's Avatar
Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,513
Default

Quote:
Originally Posted by BillL View Post
Your 650 unit was not that old either!?!? Right?

Back flying with a happy pilot and panel. - - - priceless
Bill,

The unit was purchased in mid December of 2012.
__________________
Brantel (Brian Chesteen),
Check out my RV-10 builder's BLOG
RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook
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  #6  
Old 07-05-2016, 07:53 PM
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Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,513
Default GA 35 combined list of install recomendations

Here is a compiled list of GA 35 install recommendations and other info that I gathered throughout my ordeal that many experimental builders/installers may not be aware of. There could be more details that one should know about so please get your hands on the latest manual just to be sure but here is a good list to start with:
  • Follow your receivers recommendation for minimum coax length between the antenna and the receiver. This can vary depending on the unit and the type coax you use and the number of connectors/adapters involved.
  • For lightning protection, Garmin recommends that the antenna be installed at least 51.2" aft of the nose of the aircraft.
  • Mount the antenna as close to level as possible with respect to the normal cruise flight attitude of the aircraft.
  • The antenna should be mounted in a location to minimize the effects of airframe shadowing during typical maneuvers. Typically mounting farther away from the tail section reduces signal blockage seen by the GPS antenna.
  • The GPS antenna should be mounted no closer than two feet from any VHF COM antenna or any other antenna which may emit harmonic interference at the L1 frequency of 1575.42 MHz.
  • The GPS antenna should be mounted no closer than two feet from any antennas emitting more than 25 watts of power.
  • To achieve the best possible low-elevation antenna gain (by minimizing pattern degradation due to shadowing and near-field interaction), the GPS antenna shall be mounted with clearance from other antennas, including passive antennas such as another GPS antenna or SiriusXM antenna. When practical, installers should use 12 inch center-to-center spacing between antennas. If 12 inch spacing is not practical use a maximum center-to-center spacing from adjacent antennas, but never less than 9 inch center-to-center spacing. Spacing less than 9 inches center-to-center results in unacceptable GPS/WAAS antenna pattern degradation.
  • To limit degradation by windscreen effects, avoid mounting the antenna closer than 3 inches from the windscreen.
  • For multiple GPS installations, the antennas should not be mounted in a straight line from the front to the rear of the fuselage to prevent a lightning strike from damaging both antennas. Also varying the mounting location will help minimize any aircraft shading by the wings or tail section (in a particular azimuth, when one antenna is blocked the other antenna may have a clear view).
  • The max temp rating of the antenna is 185°F and installation under the cowl of a typical RV most likely exceeds this temp at times so Garmin frowns on this location...
  • The antenna should be installed on a flat surface to prevent warpage of the base of the antenna.
  • The antenna must be installed using the screws provided to prevent damage to the antenna cap.
  • The antenna must be installed using no more than 15 inch pounds of torque on the screws. This is a very small amount of torque and can easily be exceeded by a typical person. Exceeding this torque can crack the antenna cap resulting in moisture entering the antenna causing it to fail. Use of a torque screwdriver is highly recommended.
  • Starting with serial number 110,000 and above, a change was made to the antenna cap material to help prevent damage from over-torquing the mounting screws. This does not mean that ones older than that will fail/crack if installed properly, the change was made to provide additional insurance against cracks.
  • If the antenna fails, it has the potential to start oscillating and causing interference to nearby GPS's. It seems that portable GPS's have the potential to be more vulnerable to this interference. You can verify the GA 35 is the source of the interference by turning off the receiver connected to the GA 35. If the other GPS's come back online, most likely the GA 35 was the cause and it has failed and should be replaced.
  • One should always check the coax and connectors for proper conductivity and lack of shorts. Also check for ~4.5-5VDC at the antenna end of the coax. It should be a nice steady regulated voltage when the receiver is turned on.

If you want to see what a GA 35 looks like inside, here is the link for your entertainment. Keep in mind that these units are sealed and to open one means you will destroy it and it will void your warranty. Do not try this at home...
__________________
Brantel (Brian Chesteen),
Check out my RV-10 builder's BLOG
RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook

Last edited by Brantel : 07-05-2016 at 07:57 PM.
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  #7  
Old 07-05-2016, 08:23 PM
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Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,513
Default GTN Troubleshooting hints

If you ever start experiencing reception issues with your GTN, here are a few hints that may help you narrow down where the issue is. If you power up the GTN while holding down the HOME button, you will enter config mode and from there you will be able to find the diagnostics for the unit.


If you ever see this message, ensure you check your coax and connectors for proper conductivity and lack of short circuits. Also check to ensure you have ~4.5 to 5.0 VDC at the antenna end of the coax. This should be a nice steady regulated voltage anytime the receiver is turned on.



If that is not the problem, as soon as you get the message, reboot the GTN by cycling power and check to see if you have this condition:



If you do, most likely your GPS board is failing to properly communicate to the main board and Garmin will need to have a look at it.

Here are a few more indications that mean that most likely your GPS board is not properly communicating to the main board:







If you don't have any of those indications, try borrowing another GA 35 antenna and give it a try before assuming the problem is in the GTN unit itself. I also highly recommend getting Garmin Tech support involved as soon as possible...


Additional info:

In my case all communications would be normal when the GTN unit was at ambient temps and the ambient temp was below ~95°F until the unit warmed up to operating temperature. This is when the failures would start happening.

@ 80-85°F ambient the failures would start after about 36 minutes of run-time on the unit. Upon loss of signal, the unit would usually try and succeed in obtaining a lock at least 3 times before failing completely.
@ 85-90°F ambient the failures would start after about 23 minutes of run-time on the unit. Upon loss of signal, the unit would usually try and sometimes succeed in obtaining a lock at least 3 times before failing completely.
@ 90-95°F ambient the failures would be almost immediate and the unit would go straight to the GPS receiver has failed message.

This was 100% repeatable.
__________________
Brantel (Brian Chesteen),
Check out my RV-10 builder's BLOG
RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook

Last edited by Brantel : 07-05-2016 at 08:33 PM.
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  #8  
Old 07-06-2016, 08:51 PM
Hooverra Hooverra is offline
 
Join Date: Jul 2016
Location: The Plains, VA
Posts: 4
Default

Slightly on topic, I had an intermittent reception on my 396 in my 7A. After replacing the antenna and much fuming I determined the issue was the new panel mounted USB charger. My antenna was mounted under a fiberglass access panel between the windscreen and firewall where it worked well for some 400 hours. I have now shielded the USB charger with a chunk of ferrite around the DC input. It seems OK now but I don't have more than a couple of hours on it so far.
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