Why did I crash? servo surgery

[djamgils]

Yesterday I crashed my Trex700N for the first time. Just replaced the motor bearings so I was happy that everything was working perfect during the first flight.

The second flight ended quickly in a crash. After lift off I did 2 pirouettes and then I wanted to fly away. So I gave a bit of forward nick and after that the heli didnt respond anymore and it went down nose first.
I dont know for sure if only my elevator function didnt work any more or if everything stopped working. It seems like that throttle hold did work just before the impact. and the engine was off when it was on the ground.
A picture of the wreck
http://img96.imageshack.us/img96/9350/18072010272.th.jpg (http://img96.imageshack.us/i/18072010272.jpg/)

On the workbench at the field everything worked except for the elevator servo.
After disassembling the elevator servo I found that a Mosfet was fried, it even left a melt mark on the plastic cover.
http://img841.imageshack.us/img841/4607/19072010274edit.th.jpg (http://img841.imageshack.us/i/19072010274edit.jpg/)

Now I am wondering what exactly happened. The mosfet is rated for 10A continuously and 30A spikes. So did it frie by accident or did it draw more then 30A? Why did it draw more then 30A, was there a short in the motor? How can I check that?
Can I disassemble the servo any further, I dont see how?
If the servo took more then 30A it would most likely put my voltage regulator in overload protection. But apparantly it reset fast enough so it did do the throttle hold/cut.

I would like to know what the exact cause was so I might be able to prevent it in the future.

Some basic info
Align DS610 on swash
Futaba T8FG
Flighttech 8A lineair voltage regulator

[Helico-pteron]

Sometimes electronics fail without any warning or explanation. I've seen practically every brand of servo fail for one reason or the other.

Brush yourself off and rebuild.

Sorry about the crash.

How old were the servos?

[f22warzone]

Dude that's a bummer about the crash.....

I happen to have some 610's that were fired with 40v (faulty bec pro) and will look at the board, if that chip is still good i can cut the chip from the servo ( i just want the gears) and ship you that if you want to try it out to get the servo to work again....Idk if i would trust that servo again but it would make a good spair .... pm me if you want to work something out

Best of luck on the rebuild

[djamgils]

thanks for the offer f22warzone but I will replace all 3 servos just to be sure. I presume the amp spike happened because of short circuit in the motor. so it wont help to replace the mosfet.
Does anybody know how I can take the motor out of the servo or at least check if the motor is still working?

I bought the heli second hand, I have flown about 7 gallon with it and my guess is that the previous owner flew maximum of 4 gallon with it.

If the servo pulled more then 10A to get that mosfet blown is it then possible that the voltage regulator is also damaged? Or does it have a good overload protection?

I already started rebuilding the heli, it sucks to crash but hopefully this crash hasnt dented my confidence as much because it wasnt a pilot error. To bad I just sold my backup electric heli and am waiting on my new protos to arrive. On the other hand, this weekend I will go to the 3d Masters so I wouldnt have flown much myself.

[djamgils]

I have found a way to destructively open the servo, now I definitely need to buy a new servo. :)
http://img830.imageshack.us/img830/3135/19072010276.th.jpg (http://img830.imageshack.us/i/19072010276.jpg/)

It cant be seen very clear on the picture but there are some black marks on the inside of the windings. When I use a multimeter to measure contact I get contact between the black spot and the axle that makes the electrical contact. Also I cant measure (maybe it is me) differences in resistance between the different coils. I dont know the exact word for the part that takes care of the phasing of the different coils.
http://img831.imageshack.us/img831/9033/19072010275.th.jpg (http://img831.imageshack.us/i/19072010275.jpg/)