Pitch Trim DA400 GFC700

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Leesommer
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Re: Pitch Trim DA400 GFC700

Post by Leesommer »

Well did A short flight over to Tipton and everything seemed to work pretty well after cleaning.. so we'll have to see if we have luck on a long flight
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Leesommer
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Re: Pitch Trim DA40 GFC700

Post by Leesommer »

Well it acting up again... Tried cleaning the block, contact clearer on the trim switch on the stick. But now it won't even move the trim wheel during preflight. Sometimes if I shut off the master, turn it back on, wait for the PFT flag to go away on the PFD it will work.. Really a pain. When you have autopilot on it won't hold altitude or if it does it starts seeking up and down... I'm now thinking the switch might be dicey or could it be the pitch trim servo?
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Re: Pitch Trim DA40 GFC700

Post by dmloftus »

Leesommer wrote: Tue Dec 07, 2021 10:41 pm I'm now thinking the switch might be dicey or could it be the pitch trim servo?
I'm having a similar issue. My trim switch actuates the trim consistently in the nose down direction, but is intermittent or nonfunctional in the nose up direction. The trim wheel moves back and forth relatively easy by hand and the GFC700 autopilot works fine, easily moving the trim wheel back and forth so I'm thinking it's a switch contact issue. I tried to pop the trim switch out of the pilot center stick to see if there were any open contacts that I could spray with contact cleaner. Once I removed the two retaining screws, I tried to lightly pry the switch housing out of the center stick handle. But the wiring harness connected to the backside was very tight so I couldn't pull the switch out more than about 1/4" clear of the handle. I don't want to yank on it too hard for fear of damaging the wiring. Anyone removed this before and know how to relieve the tension on that wiring?

With the amount I can see, there are a couple of microswitches that look like they are sealed in plastic casings, so doubtful spraying contact cleaner at them will do much. Ideas?

This issue also got me thinking - which breaker would you pull in case of runaway trim? I don't see a breaker specifically for the trim, so I'm guessing AFCS?
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Trim Switch 2 small.jpg
Trim Switch small.jpg
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Don
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Re: Pitch Trim DA400 GFC700

Post by Don »

If you don't already have one, you might want to get a breaker ring and attach it the AP breaker so you find it fast. My plane was delivered from the DAC factory with a white ring already attached.
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Leesommer
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Re: Pitch Trim DA400 GFC700

Post by Leesommer »

My diamond is in for annual now. They're going to check the bridal cables and a few other things. But if that doesn't resolve as an answer then I'm taking it to a Garmin shop.
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Re: Pitch Trim DA400 GFC700

Post by Rich »

Leesommer wrote: Tue Dec 21, 2021 8:38 pm My diamond is in for annual now. They're going to check the bridal cables and a few other things. But if that doesn't resolve as an answer then I'm taking it to a Garmin shop.
The pitch trim servo does not use a cable bridle, but rather a drive-shaft and chain linkage to the trim wheel. Years ago I corrected a problem where the bolt (noted by the arrow in the picture) that connects the upper U-joint to the sprocket shaft was intermittently hanging up on a piece of excess upholstery leather underneath the copilot seat. It was tricky to identify the problem, which was uncovered by some wear in the fold of the leather. This caused behavior similar to what's being described. I trimmed that excess away and that got rid of the problem. I assume the GFC 700 PT servo uses the same linkage.
Pitch Trim Linkage.jpg
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Leesommer
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Re: Pitch Trim DA400 GFC700

Post by Leesommer »

Thanks Rich I will definitely have them take a look at that once they're working under the seat
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Re: Pitch Trim DA400 GFC700

Post by Leesommer »

Well, to close the story hopefully. Went to Delta Fox at HEF and replaced the trim pitch servo... Let's hope this solves the problem. 2hrs after and no issue.
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Re: Pitch Trim DA400 GFC700

Post by Leesommer »

Sorry for such a later follow-on reply... the replacment servo did the job.... No issues even a year later.

Lee
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