Hi all,

So my APM 2.6 is dead, whether powered by the 3DR PM, USB, or ESC's through J1 (i normally do not use J1, I temporarily hooked it up - with only one ESC 5V input - to see if it would power the board), nothing will register - no LED's.  

I think that it died due to back EMF.  I had a small solenoid hooked up to the main battery power, activated by a small relay from an onboard arduino uno.  I was in such a rush to build it that I forgot to build a back EMF protection circuit, and I think that when the solenoid was disengaged a voltage spike went through the power module (PM) to the APM and killed it.

Here is what I know (after looking through the Eagle files from 3DR website):

-The board was working fine on battery power, then went dead (after solenoid use).  When I plugged in the USB after disconnecting the battery, same thing, no LED's.

-F1 fuse is blown (when I plug in the USB - i get 5 volts on the inside edge of the fuse - and like .1 V on the outside.

-F2 fuse does not appear to be blown

-3DR PM is functioning correctly (5.3 V output)

-As soon as I plug in the PM cable to the APM (no other cables connected to the board) the voltage of the 5 V input wire drops to around 0.2V.  (This happens with my current PM and a brand new one)

-I get a 150 ohm resistance from the 5V PM cable input pin to the ground bus pins across the board

When I plugged in the USB to the board and found the F1 fuse was blown, I decided to short across the fuse (since I was now inputting a known good voltage source) and see if the board would come alive.  Yeah i know, never a good idea to short across a blown fuse.

Once I shorted F1, the surface mount component which I point out in my attached picture turned red and started smoking :( .  

I am unable to locate this component though on the Eagle file, and would like some help in identifying it, and why it would have issues with a good power source.  I downloaded the file from the 3DR APM 2.6 site - but the version in Eagle says 2.5.2.  There appears to be no component between the USB micro and the row of adjacent pins on any of the board layers.

In summary here is what I'm looking for:

-What is the circuit component in my picture?

-Can my board be salvaged?  It's only a few weeks old! :(

Thanks for your time!

Nolan

APM.JPG

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Replies

  • That is a mystery part..

    3701708280?profile=original

    I turned off multiple layers in the Eagle file for  2.5.2 and cannot find that part. F1 is there. So is the USB connection, the pads for the connector rails right of the USB but, nothing where I have put the green rectangle.

    Refresh my memory. Is this a 3DR APM or one from another source?

    When did you purchase it? Is it actually a 2.6 rather than 2.5?

    There are several part beyond the connector rails right of the USB that do not show up on the de-layer Eagle file.

    -=Doug

  • Yes, you definitely are learning about electronic failure points.

    Something was definitely awry to cause the smoke to get out of that part...which I cannot find on the Eagle drawing either. My gut response is that it is a capacitor, shorted, and that is why it went nuclear on you.

    When you have a failure like this, it is best to remove ALL connections to the pcb except the power, PM cable in this case.

    Something external to your APM could have failed and lead this condition. Leaving everything connected would only confuse the situation.

    Let me see what I can find out about that unknown part. If a cap, you might be able to live without it, if shorted.

    Another cap jumpered in on the closest rail points would work fine. Most likely, if a cap, it is there for noise control.

    -=Doug

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