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Electric trim blowing fuse

homeap

Member
I have a 2012 RV-12 that I purchased flying one year ago. When I turn on the master it immediately blows the electric trim fuse. I have looked in the panel for burnt wires and did not find anything. I have the Dynon Skyview touch system with auto pilot. I will be looking at the KAI as well as wiring schematics but I wanted to see if there were any known areas or suggestions that could cause an issue. I greatly appreciate your input.
 
Break an old fuse apart to get the metal terminals. Solder a wire to each terminal and plug the terminals into the fuse panel. Now connect a test light to the wires that you soldered. Use a test light that does NOT have an internal battery. Possibly this one from Harbor Freight: https://www.harborfreight.com/612v-circuit-tester-with-5-ft-lead-63603.html
When you turn on the master switch, the test light should illuminate if there is a short circuit. Now watch the test light as you wiggle wires and disconnect D-Sub connectors.
 
homeap - You're fairly new to the forum, so I'll just pipe-up here and tell you Joe is excellent at electrical troubleshooting. He'll stick with you until you find and fix the problem. VAF is your friend....
 
Joe and Jim,

Thank you so much for the input, I will purchase one from Harbor freight and get started. If you think of any other suggestions, let me know.
Thanks again!

Russ
 
Russ,
Below is a schematic of a RV-12 stabilator Trim circuit.
This version may or may not be for your aircraft. It is the only SkyView version that I have.
 

Attachments

  • Trim Circuit.png
    Trim Circuit.png
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I would remove the tailcone fairing and carefully look at each wire that connects to the trim servo motor. These are very thin wires and one could easily be shorting on a nearby ground.
 
Russ, Search Amazon for "B01H70U690". It is an automotive circuit tracer for $27.90
I don't have this one, but it looks like it can help find a short circuit.
Connect it as I described in post #2 above, instead of a test light.
 
I wouldn't discount the Ray Allen trim servo itself. Internal workings of the servo are minimal at best...
 
Also check the service bulletins, there is a limited number of hours allowed on the trim motor.

1.A bushing needs to be added, to the shaft, to prevent bending or flexing.

2. The motor needs to be replaced outright with an upgraded trim motor, after so many hours, not sure if it's 600 or 1000.
 
It is unlikely that the short circuit problem is in the tail because the trim fuse blows when
the master switch is turned on, even though the trim switch is not pressed.
 
I’ve got the same problem with aileron trim. Started while doing the annual. Is it true that 70% of maintenance is caused by 70% of maintenance? Trouble shooting now. Ray Allen trim servo checked out OK when I unplugged it and hot wired it through a 1 amp fuse. Deeper dive tomorrow.
 
Is it true that 70% of maintenance is caused by 70% of maintenance?

Sounds about right. A great deal of corrective maintenance is required due to errors made performing preventative maintenance. Of course, the downside of skipping the preventative maintenance is causing a condition that is beyond the scope of maintenance.

Round and round we go……
 
I chased down all the wires and disconnected the servo and still could not locate a short. I talked to Tony at Vans Aircraft RV 12 electrical expert and he indicated he thought it was in the module control box. I have sent that off for repair. Let’s hope that’s it!
Thank you all for your input, it has been invaluable!

Russ
 
Finally determined the Ray Allen RP3 trim indicator in my aileron trim circuit was causing its breaker to trip, so, I removed it opened it up to check for any obvious defects - found none. When I talked to Ray Allen about this they didn't seem to surprised and offered to send me their RP4 at half price - the RP3 is no longer made. The panel cut out will have to be elongated about 80 thou (file time) but at least mounting holes are the same. Wondering if I should replace the elevator trim indicator at the same time in case its days are numbered to.
 
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