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  #1  
Old 04-13-2022, 05:35 PM
texdog texdog is offline
 
Join Date: Jan 2013
Location: Fredericksburg, Tx.
Posts: 410
Question GRT trim indication

GRT trim indication wonít move. The electric trim on the hat switch works fine. It is a Sport SX and has been working for 10 years. We have had the SX out for an emag installation and the EIS out for the pin installation for the second RPM indicator. I donít know if the trim indicator gets itís information from an aux input or where. I would appreciate any ideas from the brain trust.

Thanks
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  #2  
Old 04-13-2022, 05:49 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
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It gets its data from an external linear resistor; data goes into one of the Aux inputs on the EFIS. EIS not involved. Depending on how the linear resistor is wired (does it get power directly?) you may have to activate a bias resistor in the EFIS set up.
Edit: Ignore this, I was thinking of flap indicator.

Last edited by BobTurner : 04-15-2022 at 07:01 PM.
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  #3  
Old 04-13-2022, 08:38 PM
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Isaac Isaac is offline
 
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Location: Peoria, Az
Posts: 176
Default RE: GRT Trim indication

Texdog,

This GRT document might help understand how your trim is wired to the Sport SX. I used this implementation to wire a Sport HS and a Horizon HX installation.

https://grtavionics.com/media/Sport-Trim-Flap.pdf


You can check the GRT EIS configuration menu to determine which aux input was used. The EIS manual instructions for accessing the configuration menu are:

"To access the “Configuration Set” pages, press and hold the center and right button until the screen shows “UP DOWN NEXT” on the bottom row. The display will momentarily show the “Set Lean Pt” page while holding these buttons. This is normal. After about 5-10 seconds, the “Configuration Set” pages will be displayed. This deliberate action is required so that anyone unfamiliar with the instrument will not inadvertently alter the configuration of your instrument."

Edit: 4/15/2022 -- The Sport SX doesn't have analog inputs at least according to the document I have. Here is the paragraph from the manual:

2-6: Analog Inputs
The Sport SX does not include analog inputs, however, the EIS engine monitor provides up to six auxiliary inputs that can be used for trim and flap position.
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Last edited by Isaac : 04-15-2022 at 01:26 PM.
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  #4  
Old 04-15-2022, 10:54 AM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 2,532
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Trim position indications are a real source of frustration - not just with GRT equipment. The 5 wires going into the RAC trim servo are of very small gauge. Often they are too small to have been properly captured/crimped into connector pins. I can't tell you the number of times I've fixed trim indication problems by going to the first connector downstream from the servo and fixing connector pin-to-wire connections.

If I were in your shoes I would get a a DVM (digital volt meter). Disconnect the connector on the Sport EFIS and use the test leads and DVM to connect between aircraft ground and the middle "wiper" signal input pin to the Sport. Set the DVM to Ohms scale. Actuate the trim motor and look for changing ohms reading on the DVM. If you don't get a change then you have a discontinuity in wiring between the trim motor's position sensor and the Sport EFIS.

I would suggest the lowest hanging fruit in this case is likely a failed crimp pin termination somewhere back near the trim motor.
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  #5  
Old 04-15-2022, 06:02 PM
sf3543 sf3543 is offline
 
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Location: San Antonio, TX
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Quote:
Originally Posted by BobTurner View Post
It gets its data from an external linear resistor; data goes into one of the Aux inputs on the EFIS. EIS not involved. Depending on how the linear resistor is wired (does it get power directly?) you may have to activate a bias resistor in the EFIS set up.
FYI The flap position indication gets the travel data from an external linear resistor, usually a POS-12, I think (Assuming the Ray Allen servos are used.); however, the trim system indicator information is created by the trim servo itself, not a separate unit. (Through the Green, Orange and Blue wires. The two white wires actually power the servo motor and go directly to the switch/ relay.)

Anyway, assuming that your wiring is correct, since you said it has been working all along, we could assume the problem was likely caused when you had the EFIS and EIS out.
I would first look closely at the connectors and see if a pin has been pushed back/out, a pin bent or broken off, or if a wire has been cut or pulled loose. Look at the EIS connector as well as the EFIS connector, particularly the serial wire pins and the Serial port pins you are using for the trim system. Also inspect the wires themselves for cuts or abrasions.
If that doesn't work, I would verify that the programming in the EFIS/EIS didn't get changed accidentally.
If the trim system is actually working, but no indicator on the EFIS for both pitch and roll, when you used to have it, I think that pretty much narrows it down to wiring at the EIS/EFIS or programming. Especially since it happened right after you worked on it.
Good luck.
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  #6  
Old 04-15-2022, 07:00 PM
BobTurner BobTurner is offline
 
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You're right; I mis-remembered.
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  #7  
Old 04-16-2022, 05:44 AM
texdog texdog is offline
 
Join Date: Jan 2013
Location: Fredericksburg, Tx.
Posts: 410
Thumbs up Trim indicator

You folks do wonderful work, thank you. Iím electrically challenged, but partner can help me do this. Again thanks. I will let you know what we find.
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  #8  
Old 05-13-2022, 07:32 PM
texdog texdog is offline
 
Join Date: Jan 2013
Location: Fredericksburg, Tx.
Posts: 410
Thumbs up Trim indication follow up.

The problem was a broken wire in the 5 wire bundle from the trim tab to the indicator. The trim worked fine, but the pilot didnít know where it was without visual inspection. We ran a parallel wire from the Ray Allen to the EIS and it works and indicates correctly. A lot of work from my partner to run the wire and a fellow RVer to connect the wires. We had a Ray scholarship student crawl in the tail to tie everything up. Thanks all for your help.
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L19 sold
ATP/FE/CFI 10 Type Ratings.
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