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.


You need to be a member of diydrones to add comments!

Join diydrones

Replies are closed for this discussion.


    • So you did precisely what was stated not to do?  Did you even install the capacitor first?

      • 100% exactly as stated not to do (but should be able to do... but lets not beat that dead horse).

        Capacitor not yet, next step.

        Test hover and quick flight around went fine.  Only one single motor spun upon arming, need to read back on that feature, ESC's might need recal. if all are supposed to spin but that is outside of the topic of this thread.

        • I actually agree that the board design should be such that this does not cause a problem.  While it may be true that "back in the day" hot plugging was bad, it is common practice now in consumer electronics.  If we can achieve hot-plug robustness, then we should.

        • And just to finish this off in case a future user has problems, re-cal of esc's fixed the arming issue.  Now all four spin when armed.

        • By the way Rob, we have a saying in our industry for dum ass moves like mine:

          "Every day programmers are making programs more and more idiot proof.

          Every day the Universe is make more and more idiots.

          So far the Universe is winning..."

          Enjoy the chuckle.

    • Should have qualified, this time it was powered by a lipo battery before the usb was plugged in.

      Regulator fixed again, now going to try the painful method of not doing a damn thing unless all power is off, even connecting simply Rx connections.

      • Ouch I wasn't expecting this Tim:(((

        At least you can replace it in a few minutes. Now I want to understand one thing: did it blow before even you start connecting anything? Or after?

        If it is after you have connected something, then the reason is obvious. But if it did before, then I cannot explain it.

        I would say try one more time  just like Randy advised and if it blows again, then give it a one last chance (hoping you ordered at least 3 spare regs.) but this time go back to previous firmware where everything was happy and see if that will make any difference. Just to make sure... 

        • Alex -

          This is EXACTLY what I was thinking MIGHT happen ESPECIALLY if the culprit is, as I suspect, large low-ESR capacitors in the device being attached to the APM. Now that we actually have folks with electronics experience looking for the failure in a controlled environment, we may be able to replicate the circumstances with more than just one or two users.

          Tim -

          Have you done the recommended "100uf ceramic cap at A2" mod? If not, please do and if you're feeling brave, try again with a hot-plug event.

          Also, just out of dumb curiosity, how much did your parts order come to, and for how many pieces?


          Together, we CAN build the perfect beast.

          • No problem Alex, will dig back and found the mod and perform (don't think I have any spare caps so I'll order some from Digikey).

            Have 3 more regs so can do more testing, though one of the lands is getting a little loose (They just don't make PCB's like they used to in old days.  We used to be able to DRILL out through holes to enlarge them without tearing the land from the board...try that with todays!).

            Thankfully that land is connected to the cap beside it so if it does come loose it's an easy jumper to fix.

            Cost was 16.81 total CDN to my door overnight FedEx for 5 regs ($1.50 each).

            • No need to dig back. All is here :)))

This reply was deleted.


Shivchand Jaysaval liked Shivchand Jaysaval's profile
Aug 25