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Trim Failure
My -8A?s Ray Allen trim failed. The relay clicks, but the servo doesn?t run. My A&P checked everything (I?m not much good with electrical stuff) and said it was definitely the relay. So I bought a new relay, replaced it, and same same.
He?s made it clear that he doesn?t like working on electrics and avionics. What do I need to do next to figure out what the problem is? I?m fine with just hiring someone who knows what he?s doing. I?m near Ft. Pierce, Florida. Frustrated with all the squawks that keep popping up. Total hangar queen and waste of money so far. |
Check output of relay with it activated to see if you are getting voltage.
If not you have a power issue (wiring to relay or relay itself). If you do have output voltage it's a wiring or servo issue. |
Jump a 9 volt battery right at the servo. If my memory is correct, its the 2 white wires, no stripes. Reverse polarity to make it run the other way. That will tell you if its the servo or to keep looking.
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Most RVs have this trim system. Find a builder near you to help. He will know what to look for.
Carl |
Often folks add one or more resistors to slow down the swervo travel rate so that trim is not overly sensitive. Is your failure just on teh ground with the master on, or when your engine and alternator are running? THe lower voltage without the engine running could be the difference in whether the swervo operates or not. If thats not it, you may need to track down where you are losing voltage.
Erich |
The trim failed in flight - nose up on climbout. It stuck in that position - 30 mile flight home pushing the stick forward.
I?m stepping over to the hangar to try these suggestions. Then it?s just fixing the empennage gap fairing (stripped screw threads - Van?s says put in nutplates, but I see folks here used pulled rivets) and a couple other things. |
Relay output is good, and the servo is working just fine. Now I just need to figure out where the wiring is broken.
So many lessons being learned here. #1 is hire a recognized expert in the type, spend more on a deep inside-out prebuy and say no if it?s not darned close to perfect. |
easy places to start
Quote:
Check the grounds. Blown fuse, C/B? |
Everything seems to be good up to the tail. I found a loose pin on a small computer-type connector (Dsub or Molex maybe) between the wire bundle coming from the cockpit and the servo. Is there any functional or regulatory reason to not use butt connectors? I don?t have the tools to crimp and set pins in the other connectors. Looks to me like these are wires that won?t ever need to be disconnected, so regular crimped connectors should work.
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Butt connectors should be fine. The servo wires are very thin so after they are stripped, you can fold the wire over the insulation and crimp that. It will stabilize the hair thin wires.
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