One motor runs as soon as mQX is plugged in

[burnoutboy]

I was flying with he DX6i for the first time and experimenting with rudder rates and she just dipped left and SLAMMED into the ground. Hit so hard the battery came disconnected!

Well I put her all back together only when I plugged in to initialize one of the motors immediately began to spin at about 1/2 throttle. It does it before initialization with the TX on or off. I've rebound, bound to the MLP4DSM, and bound back to the DX6i and still nothing. Nothing gets warm nothing looks burnt. All trims and sub trims are zeroed.


Any ideas?

I'll get the new board if need be but want to avoid it if I'm missing something dumb.

[clough42]

I don't have an mQX, so I'm speculating here, but that sounds like a burned FET. This could have caused the tipover in the first place.

Other possibilities:

1. Cracked solder joint on the board.

2. Debris shorting the board.

3. Damaged wire insulation allowing a current path.

[burnoutboy]

Checked for debris, tried multiple motors to make sure no short in motor wires.

Can a fet fry for no reason mid flight??

[clough42]

I really can't offer you much here. I just recognize that behavior from numerous postings where an mCP X tail runs continuously. Usually it's a short in the tail wires caused by a broken boom that burns the tail FET. After replacing the tail, the motor runs continuously.

[burnoutboy]

That was my first thought honestly but the FET doesn't appear burnt on the surface and doesn't get hot. HMMMMM..

Maybe I'll just try replacing it and see what happens.

Does anyone know if the FET for the main motor on the mSR X is the same one needed for the main on the mQX?? Any leads on where to get one? I wonder if topcopter has em.

[poor_red_neck]

I dont have a mqx, but post a high res closeup pic of it and I'm sure I can find it for you.

Do you have experience with surface mount soldering? I have a SMD rework gun/station. Shoot me a PM and ill help you out.

Sent using TapaTalk on my HTC Evo 3D
Please excuse spelling/grammatical mistakes due to fat thumbs.

[burnoutboy]

Will do. I'll break out the DSLR today.

I don't have a ton of experience with surface mount, other than soldering/desoldering ESC connectors and doing wiring to board, but I have enough and I'm confident I can get it done.

I'll post that pic around 5 tonight.

[burnoutboy]

BAH, I forgot. I'll try and get it tonight.

[burnoutboy]

Originally Posted by clough42

I really can't offer you much here. I just recognize that behavior from numerous postings where an mCP X tail runs continuously. Usually it's a short in the tail wires caused by a broken boom that burns the tail FET. After replacing the tail, the motor runs continuously.

You da man!

So it looked totally fine but I figured what the hell it's like $1 for a new FET so I gave it a try. I'm 110% good to go now. Thanks a ton man! Blown FET was my first thought but since I never saw any smoke and it didnt get hot at all I was doubting myself. Took your advice and I'm back in the air!

[gewing@sssnet.com]

have any pictures of this operation?
I hit the ground and have the same issue. New board on the way, but would like to fix this one.....
Thanks

dx6i w mqx

[burnoutboy]

No pics of the operation but I'll certainly post a pic of my repaired board with the new FET in place. I get off at 9 tonight if I remember I'll post it up after I get settled in at home.

[Pfloyd]

Sounds like you have a cracked main board.

[burnoutboy]

LOL no one reminded me to post pics.

PFloyd, why do you say it sounds like a cracked main board? Sounds like it's probably just a burnt FET to me.

The circled FETs are your motor FETs and the one circled in yellow was the culprit on my board.

[Pfloyd]

A lot of problems (especially with the MSR) is a hairline crack in the 5n1).