My APM2 powers from the input rail with the jumper off, but will not power from the output rail (pin 3 esc) with the jumper on. How do I diagnose this to determine if it's a fault board?



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Hi Adam,

First, ensure you are pulging the wires in the rigth way, allways +5v (red wire) to center, and -v (black wire) to the edge.So yoiu got to roll it 180º from avobe to change from one rail to another. You can see the pins sing here:

i haven´t seen the APM2 board scheme or having the pleasure of touching one but i think the jumper will joint your output and input +5v pins. To test this, you can use a multimeter, if one of the jumpers pins has continuity with une of the rails pins (whatever) and the other pin has continuity with the other rail pins, the jumper will joint theses lines of pins, Test your jumper swicth continuity (The little plastic part you use to put it on) can use a piece of wire core to put it on over the jumper board pins to test it too.

Any way, Measure the voltage between + and - pins in input rail whem "powered" from output rail and jumper on. If you got +5v +/- the jumper is supous to be working and you got power on input rail, so anything between jumper and main board must be wrong.

Hope it usefull for you.


Hello, I have a similar problem in APM2 I have 5v output. coming from a BEC.

The problem is that when you connect a servo, according to wiki, negative on the outside.The low voltage of 5v to 1.40v.
With the consequence that there is no movement in the servos.

Are you sure the jumper is on the right pins and is seated correctly?

If, thanks Chris, I just concluded that I had to feed from the output of the APM and the entryand Rx. Thanks, all working correctly now.

My board behaves the same way.

With the jumper on, I'm only getting 1.32V on the input rail when powered from the output rail. But, strangely enough, when powered from the input rail and with the jumper on, there are full 5V on the output rail.

Looking at the bunch of similar posts.. maybe a batch of boards got messed up somehow (like a diode being inserted the other way or something)?

Andrew: Please contact customer support ( for a RMA.

And are you powering from output chanel 3 ?

I have a separate UBEC and I'm connecting it's output to a free channel on a rail.

try to connect it to output 3 just in case, as described in the page, just to check !


Alright, I've tried that, and, well, it's the same story when using output 3 or any other channel. The juice just won't go from output to input rail, but happily flows in reverse direction.


Thanks! But I'm actually okay with it. I have no need to power the board from the output pins (yet..)

And we have waited long enough for the boards, I just want to fly this thing already :)

I know this is kinda simple, but...

The pins for the jumper are 2mm spacing, and not the standard 2.54mm like all the other pins on the board.  Are you using a properly sized jumper?

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