rleffler

rleffler

Well Known Member
Over the last month I've been troubleshooting a problem that was induced by a documentation error in the GTN650/750 AML STC Installation manual.

For connector P1004, which is detailed in section 4.1.4 of the installation manual the illustration showing "looking from the Pilot's seat" and "looking AFT towards the Pilot's seat" have incorrect labels. The labels are reversed.

In Revision 3, which is the version before they showed both views is correct. In Revision 4 and Revision 5, they are incorrectly labeled.

I was unable to locate a Revision 6 manual.

In Revision 7, they removed the two views and went back to the illustration found in Revision 3. Coincidently, the Garmin dealer that I was working with wasn't aware of a Revision 7 and wasn't notified until they reported my issue back to Garmin.

My problems started with a failure of the NAV board in my GTN650. Since the board failed, I decided to validate the wiring harness and ohm'd out all the pins. The harness was built with the Rev 3 documentation, which was correct. Not knowing any better, I created an issue when I was testing the harness using the illustration in the Rev 5 release. I couldn't see the pin numbers in the connector in the back of the stack, so I relied on these illustrations to determine the location of the pins.

So thinking I made a mistake on the original harnesss, I re-pinned the connector to it's mirror image per the illustration. Needless to say, when my unit came back from being repaired by Garmin it wouldn't work correctly. I won't go into detail on the various tests I conducted to eliminate all the potential issues as defined by the dealer I purchased the unit from. I probably put in forty to fifty hours of testing and taking my entire panel out to validate all the connections in the harness. Everything matched the illustrations in manual, which generated much frustration as to why things weren't working.

I then decided to take the unit home and build a second harness on my desk to test the unit. I forgot to mention that in during all this, I did take the unit to a local Garmin dealer and tested the unit on their bench to ensure the unit was working properly. It was, so the problem had to be localized to my aircraft.

I then noticed that the pin labels on the connector didn't match the illustrations in the manual. That's when I started researching the documentation errors.

What really got my goat is when the Garmin dealer reported the issue, the response was bascially to chastise the installer for not validating the actual pin numbers and trusting that the illustrations were correct. The table below the illustrations was accurate with the correct numbers. But my frustration if I used that logic, why would I trust any part of the documentation as being accurate.

Garmin just doesn't understand customer support and service. A simple, "we're sorry and we've updated the documentation" would have been a proper response. But there response came off as saying you should have known better and not used the illustrations to wire the harness.

I'll get off my soapbox now. My main concern was to let the community know of the documentation error, so that they don't have to repeat the ordeal that I just went through.
 
Thanks for the heads up Bob. I'm going to be getting deeper into my 650 pretty soon so I will be sure to double check the pinouts.

I have been led down the "primrose path" by faulty documentation many times in my career... It can be a real time suck.
 
Just another thing to consider when chasing goblins like that, something we would do pretty much automatically once we know for sure it's an issue with your plane (and in this case the unit didn't come from us), is to check the wiring diagrams not only with our own in house diagrams, but also compare between Garmin Manuals. While you can use the AML/STC manual, the TSO version of the Install (preferred) manual is somewhat more concise and is an excellent comparator betwixt the two.

I took a quick look at the AML manuals all the way back to Rev2 and indeed I see that change in Rev 4 (where the label to the Dsub picture is obviously changed and wrong) but only on the picture caption at the top of the page...the actual pinout itself in the table below seems to be correct across all the rev's across all the manuals (at least at my first pass). Did you find a place where the pinouts were wrong?. I didn't read each rev in detail, nor compare each rev of the STC manual against the TSO manual, but at first pass they seem to be correct...

Lastly, though almost impossible to read - there are numbers physically stamped on the Dsub itself. One hint we use here in the shop is to use a white-out pen to identify certain pin numbers (like pin1,10,20, etc..) on the back before we start wiring, that way you can easily count to or from that location when inserting wires.

Anyway, things like this can be frustrating - believe me when I say we have plenty of our own "walks down the primrose path" as Michael noted! I also can't see what some TechPubs person was thinking as they obviously kept changing that caption from Rev to Rev of the manual...it's not like their captions got any better! :)

Cheers,
Stein
 
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No, I didn't purchase the unit through you Stein.

The pin descriptions in tables were always correct. My mistake was to assume that the illustrations were correct. When I was performing the testing, it was almost a year and a half after the harness was constructed. Because of the location of the connectors, my eyesight not being what it used to be, I trusted the illustrations to determine the pin location instead of the actual numbers, which I couldn't read easily.

Actually, it's the labels on the illustrations that were reversed.

Clearly, I learned multiple lessons on this. I hope this posting can help others from making the same mistakes that I did.

Marking pin one in color is a great idea. The other lesson I learned is to make the pigtails in the harness about twice as long as you think you'll need. Working on the high density connectors are arms reach under the dash is a royal PITA. Especially for those of us with bifocals.
 
rleffler said:
No, I didn't purchase the unit through you Stein.

The pin descriptions in tables were always correct. My mistake was to assume that the illustrations were correct. When I was performing the testing, it was almost a year and a half after the harness was constructed. Because of the location of the connectors, my eyesight not being what it used to be, I trusted the illustrations to determine the pin location instead of the actual numbers, which I couldn't read easily.

Actually, it's the labels on the illustrations that were reversed.

Clearly, I learned multiple lessons on this. I hope this posting can help others from making the same mistakes that I did.

Marking pin one in color is a great idea. The other lesson I learned is to make the pigtails in the harness about twice as long as you think you'll need. Working on the high density connectors are arms reach under the dash is a royal PITA. Especially for those of us with bifocals.
Click to expand...

Boy do I know what you mean...I'm half blind even with my glasses on! :)

Like I said, I can't figure out who thought changing those captions was a good idea to begin with (the first Rev made plenty good sense, and they seemed to get more confusing and less useful each Rev)! It's always tough to chase those ghosts, and one other truth....pretty much EVERY single mfgr out there has or had similar flubs somewhere in their manuals (in fact it happens more than one might think) - so it's always a good idea if you're in the middle of a head scratcher to either cross check it with an older version, with a similar version, or with your own.

Cheers,
Stein
 
Good evening Bob,
My sincere apologies you had to endure this problem. We found out about this issue early on after the release of the manual and as quickly as possible actually released an Install bulletin (IB 1332) in June 2013 identifying this issue to make all of our installers aware.
My apologies as well if this was perceived as scolding the dealer we hope that all of these bulletins are routed to the right person but as we've found out over the years especially in large shops it's difficult to guarantee this. Regrettably getting the STC manual updated quickly has to wait until the next release which is why in some cases the TSO manual is faster with updates.

I do my best to monitor the forums and assist (I'm currently on 6 of them) however in some cases don't see messages like this quickly so if there are any concerns or questions please feel free to send me a private message and I'll be happy to jump on it and assist as quickly as possible. We want to do everything possible to make your Garmin experience a pleasant one.

Best Regards,
 
What kind of errors?

Bob - would you mind sharing what kind of errors you encountered when the unit was incorrectly wired?

Is there way to determine, without pulling the unit out, if the wiring is fine?

My unit was wired by the dealer, and I wanted to make sure that error was not made (I dont have the support of the dealer, so going to him with questions is not an option).

Thanks in advance!
 
Airzen said:
Bob - would you mind sharing what kind of errors you encountered when the unit was incorrectly wired?

Is there way to determine, without pulling the unit out, if the wiring is fine?

My unit was wired by the dealer, and I wanted to make sure that error was not made (I dont have the support of the dealer, so going to him with questions is not an option).

Thanks in advance!
Click to expand...

You are asking a loaded question, in which the symptoms will only match if the same error occurs.

With P1004 wired in a mirror image backwards, the power pins are in the wrong location and the boards will not power up. The GTN650 gave the message that the NAV board failed as well as the Glideslope failed.

Yes. In Revision 7 of the manual, the illustration is correct and it displays the view that you see if you are looking into the tray from the pilot's seat. You can also ohm out the pins to ensure that they are going to the correct location in their respective destination connector.

Btw, this was the trap that got me into trouble. Even with a magnifying glass, I was unable read the pin numbers on the connector at the back of the installed tray. I depended on the illlustrations to ensure that the pins were in the correct location.

During the troubleshooting phase, I took photos of the connectors, provided wiring diagrams, and my wirebook detailing exacting how the harness was wired. My photos matched the incorrectly labeled illustration. Neither myself, nor two Garmin dealers caught the error. We all got caught with counting pins holes and making sure that they matched the illustrations. Nobody thought to compare the illustrations with the pin numbers on an actual connector. It wasn't until I pulled the tray and the unit out of the aircraft and took it home, that I noticed the mistake.

Just to reiterate, it was just the labels on the illustrations that were incorrect. None of the other information concerning the pin assignments were wrong.

My only recommendation is to ohm out all the pins yourself. If somebody else built the harness, this accomplishes two important tasks. You'll gain more intimate knowledge of how your aircraft is wired and you'll confirm the outstanding job of the company that built your harness.

bob
 
Wiring the GTN 650

I guess this eye failing problem is epidemic. When it came time to redo the Doll's panel with the GTN 650 and dual G3X, I took the easy route, and let Stein and his merry men do the job for me. That was money well spent!
Thanks Stein and Christer!
 
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