This is a discussion re the bad Accel, Gyro and Baro values that we're seeing with ArduCopter-3.1.  The increase in the SPI bus speed from 500khz to 8Mhz has exposed a hardware problem on some boards.  That hardware problem is that the 3.3V regulator has been blown so all sensors are running at 5V instead of the intended 3.3V.


How have these regulators been burnt out?

  • Attaching a radio receiver or MinimOSD to the APM while the APM is only powered through the USB (see video below)

  • Some clone boards seem to come from the factory with blown regulators.  3DR boards might also come with blown regulators although they do a specific check of the regulator as part of the regular QA process.
  • It is not (as far as we know) actually caused by the AC3.1 software itself, it just exposes the problem.  You could prove this to yourself by checking the 3.3V regulator (see video above) before and after the upgrade.


How can we fix the regulator?

Option #1:  If it's a new board (so that it's less likely you burned it out yourself) you could report the problem to the retailer that sold you the board and ask for an replacement.  If it's 3DR it's called an "RMA".

Option #2: if you're handy with a soldering iron you can replace the regulator yourself.  On the APM2.5.2 (and higher) boards it's not that difficult.  On the APM2.5 it's far more difficult.

3691073788?profile=originalFor APM2.5.2 : TPS79133DBVR

For APM 2.5: MIC5219-3.3YML TR

How can I stop it from happening again?

Do not connect any devices such as a radio receiver, MinimOSD, GPS, etc while the APM is powered especially while powered only through the USB cable.

Attaching a 100uF capacitor across any of the APM's radio input's 5V and GND pins will stop the regulator from being blown by plugging in a receiver.  video here!

There are very few reports of regulators being blown twice and no reports of it ever failing in flight.


Below are some graphs of the types of values that we are seeing on these boards.


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  • Developer
    You have missed the point here. The capacitor stops this, and is much simpler than changing to a regulator that does not really fit.

    I am 100% behind PK's experiment, but it must be tested, and proven that this does not happen with it as well.

    Also, what is it glued on with?
  • Paul
    Unfortunately I did not see your mod, if I had not placed the controller the way you explained in your mod. I put the v + v + the regulator with Vin and Vin old controller, its shape is much more effective. Also disconnect the USB Cable Positive to remove the risk that the accident occurs, I think it's more effective than capacitor 100 uf, 100% to reduce the possibility of feed apm by usb.Si for any reason we lose no main power supply by usb risk
  • So... funny we were just talking about Good Luck Buy a bit ago; I just received my new APM Power Module from them. 9 days to my door from Shen Zhen. Now I didn't KNOW I was buying from them; I just found a nice inexpensive PM that had good looking specs on fleaBay:


    and went with it because it was within my budget.

    Before you say it, YES, it IS a Power Module; it has 5.3V out rated at up to 3A from up to a 28V power source, so definitely 6S capable.


    As you can see here, it's built around a MP19530N adjustable regulator. This bad boy is rated for up to 3A output from up to a max of 30V; so 7S is technically possible, though such packs aren't exactly popular.

    My question is: Is this an independent design, or is it based on an authorized design I just haven't seen yet? All the ones I've seen have a separate regulator module similar in appearance to the Pololu regulator modules most of us have used for some robotic project or another.

    Power is filtered with, you guessed it, ganged ceramic caps. That little pair at the 5V output measures 48.8uf at 0.01Ω ESR!

    When I'm not dead on my feet, I'll fire up the old 'scope and see what that power looks like.



    • Paul,

      thanks for posting this. I had been looking for one that could handle 6S. I have been stuck using 5v from my ESC on this copter. I ordered 2 to give them a try.  how are yours doing?

      Something I do on the 3dr power modules is change the 4 watt  .0005 ohm shunt with 2, .001 ohm 5W resistors


      I put them in parallel to get a 10W .0005 ohm resistor which should bring the max current up to around 145 amps instead of 90a . it has been working good on the 3dr modules ive done it too.  if the new resistors will fit I will do the same on these modules.

      thanks again for posting this.


    • Then change the regulator 3.3v for my apm 2.6 LD1117av33.
      I've connected to the mission planer and everything worked perfectly.
      Will I have any problems having put the LD11117av33?.
      I have also removed the usb cable + power, if the usb vcc runs out the main power apm not hurt to not having current.

      • Did you use my LM1117 mod :

        APM LM1117-3.3 Regulator Mod

        as a guide? If so, welcome to the club. :D

        Right now, this mod is in Beta testing; I'm looking for folks to try it out and see. Preliminary testing is promising; I'm waiting for more gear to arrive to continue my work.


        • Juan, Phelec -

          Look at my APM LM1117-3.3 Regulator Mod

          It has detailed pictures of two different ways you can mount the LM1117 securely; either one would be an improvement both mechanically and electrically to what you have there, Jose.


          • Yes, I had a look earlier today. The addition of some extra caps is a good idea. Too many manufacturers like to save 5cents by leaving out those parts. As you said, the board will mostly work alright for 98% of the time, but when there is a sudden demand for more current, then the crashes or failures happen.

            In my fpv planes I add several caps throughout the system. I usually parallel a tantalum (47uF) and a polyester (.01uF) as well as the odd 2,200uF electro.  So far, no glitches causing strange and random behaviors. Each type of capacitor has it's own characteristic to handle different frequency interference and current demands.

      • Good luck, you have solved your problem. The LD1117av33 is an overkill (very large). But, if you can mount it so any vibration will not fracture the solder joints, then I suppose it is OK.

        Just be careful the weight of the LD1117av33 is large and being held just only by some small area of copper print on the circuit board. If you have connected it to firm sections of the circuit board then it should be OK.

        Happy flying for you......


          Thanks for your interest, I've attached with hot glue to prevent accidents.
          and removing the power to the USB cable also worked, no longer exposed to work with USB power under any circumstances



          A little sloppy but it worked.
          Thanks for the help and best regards.

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