Frequently asked questions are about powering an APM2.5 or why the same does not work or why it has failed.

Here is a simplified schematic showing the major components of the 5V/Vcc circuit on the APM2.5

Target Audience: Readers who do not have Eagle or are confused about using it.

You Need: Basic electronic schematic reading ability

Note that I have separated the PWM Output section into the upper left corner with a heavy purple line that is bridged by the jumper JP1 on the APM2.5. This is to emphasize that diode D1 passes current through JP1 (and drops voltage). The remaining energy is then called 'Vcc'.  Everything outside the purple corner is Vcc.

This is why the USB will power the APM2.5 when connected to a computer/USB hub. Note the fuse on the APM2.5 side of the USB connector AND another fuse on the output of D1. Another change from APM2.0 is the D4 6.0V Zener diode. If an over voltage is applied to the board, D4 will crowbar what it can to protect devices.

As with APM2.0, any 5V source connected to any of the indicated Vcc/5V points outside the purple corner (with GND of course) will power the APM2.5.

Also of note is the 'Mystery Port'. This port takes 5VDC before D1 and the fuse and is called 'JP_VCC'. Other clues to the mystery are the lines to 'ADC 12' and 'ADC 13'. A mystery indeed!

Any errors in this drawing from editing are mine.

I hope this can be used as reference for solving problems.



27-FEB-2014 Eagle files are now located HERE


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ok have taken D4 out 

power from Laptop USB  JP1 off

all voltages ok  between ground and various points  5.06v and 3.29 points 

looks all ok  yet still not connecting to Mission Planner

could put a scope on the Rx TX pins  

I use Mission planner1.2.22  latest  with mav 1

when trying to connect led A red and blue C flashes  but nothing on other LEd

one time out main red led on

and A flasing 

which UART is doing the connection via the USB ?   will try to figure out later as I have schematic now V1 and V2

The Zener is installed across the power supply to prevent damage to the board if you 

a) connect too high of an input voltage

b) connect the power supply backwards

If either of these things happen the zener will conduct and the fuse will blow. 

What is the purpose of the D1 diode? I had my power coming in from the outout rail with JP1 connected and was getting brownouts causing 1 or 2 esc to loose its signal and start to beep. I seem to have fixed the proplem by feeding the board its power from the input rail which bypasses the D1 diode.

D1 isolates the USB power from the output rail.

If you are getting brownouts then your input voltage to the board is too low.

Note: The 'Mystery Port' was revealed to be the connection for the new 3DR APM Power Module.

This schematic also works with APM 2.5.2.


im having issues powering a 2.5 as well.  usb works fine and powers the RX module plugged into the Inputs.  but when I plug in an ESC into outputs with 5v on it nothing powers up.  even IF JP1 is on or off.  bad JP1 solder job? whats the pinouts for the magic power port?  can I make a cable to power from there?  any other jumpers that I can power with a UBEC the APM with?


Sounds like you have a 'ubec/ESC with bec' connected to the APM output pins, and an RX connected to the APM input pins.

With this configuration, the only possible reasons for power not getting through to the Rx are:

(1) Jumper missing.
(2) on-board Fuse blown.
(3) supply Diode blown.
(4) O/C cables.

At a guess I would say 1, 2, 3 as most probable!

Biggest problem with the alternative power port is its small pins, IMO not man enough for use as a power socket, hard to find suitable plugs, and almost impossible to connect leads to these plugs without specialist gear. Where the APM output connectors are heavier duty, plugs and leads are readily available, already fitted to ESCs servo's and ubecs! No contest...

Why has my post been edited?????????

No point in posting here anymore!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!C

what was edited?

Sorry, senior moment, wrong forum, wrong thread...

The 'Mystery Port' in the schematic above is the Power Module port.

Click on the schematic and you can see the connector designator.

Hirose makes the connector (pcb side) and a source for it is HERE. You would have to have the female connector to plug into the board side item.


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