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By joe-fbs
#1611493
Anyone with knowledge and experience to comment on the below please? (WigglyAmp springs to mind).

Our group aeroplane has some oddities with its GTN650.

First thing is to replace the internal battery. The manual requires this to be done by a dealer (we use the aeroplane for IFR so need to maintain it to the book).

Assuming that does not fix the problems, detailed below, it needs some investigation. Our usual maintainer has done the basic checks of wiring so I think it is probably not something obvious.

Details of the problem:
After power-on of the aeroplane, the GTN takes about fifteen minutes to come to life. Once on, it acquires a position only occasionally and for short periods. The radio and VOR functions of the GTN are fine. The aeroplane did spend six months last year and three months this year not flying for mechanical work to be done. Mechanically it is now fully serviceable and back in use. Having myself flown the aeroplane several times recently, including for some two hour flights, I can almost convince myself that the more it is used the less the GTN650 misbehaves (i.e. does not take so long to start then acquires a position fix more often and for longer) almost as though not being used in some way confused it. All this seems completely irrational! I did also notice that when I landed for a quick fuel stop and the power was off for only about half an hour that the GTN came to life almost immediately on restart.

The database is currently out of date. Normally we update it monthly but I am not doing that while it is of such doubtful serviceability. I believe that this has no bearing on whether the unit works, just whether t is legal for IFR.
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By PaulSS
#1611495
I can almost convince myself that the more it is used the less the GTN650 misbehaves (i.e. does not take so long to start then acquires a position fix more often and for longer) almost as though not being used in some way confused it. All this seems completely irrational!


Not at all irrational I would say. I'm wondering if your database being out of date will in some way affect the GPS almanac, thereby taking the GPS longer to get a fix than it should. It sounds to me like the GPS acquiring its position is the problem and that's why you notice it taking longer after a lay-off than when it's been recently used.
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By Flyin'Dutch'
#1611497
No experience with the 650 but plenty with the 430 and never had any problems getting it going after any period of being inactive.
By NDB_hold
#1611517
Assume you’ve checked the electrical system voltage? (Just thinking about the way it behaved after a short shutdown.)

This is very like an issue we had with a Garmin audio panel and we ended up replacing it.
By johnm
#1611624
If the database is up to date the next thing on the list would be the antenna installation. It's very important to use the right antenna and the right cable for the GTN 650 and if it's been unused for extended period connector corrosion might be an issue??