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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  • I though you guys would like this. I received a bad board from GoodLuckBuy, and sent it back. I got the new one today and plugged it in and "Bad Gyro Health". I checked the voltage, and it was fine. I looked at the compass on the GPS board and.........


    • Looks like a bad wave-soldering joint on the one side, then the cap got knocked off from handling. Look carefully in your packaging; you may find it rattling around in there.

      If you do, take pix of it before you solder it back in; really, more hassle to get a return than a little soldering's worth. If it still doesn't work, THEN start a return.

      As far as the QC issue's concerned... I've Found Good Luck Buy is aptly named, as in "Good Luck with whatever you Buy ".

      They're in the volume business; they don't inspect anything. They ship what they get, period. If you can get past the usual "Language barrier" game the China Direct vendors ALL play, then repeat yourself 16 times even though you already answered their "Did you do this dumb-as-a-bag-of-hammers" thing or that "too-stupid-to-remember-to-breathe" thing questions in your first eMail, AND provided photos... THEN you may get to someone who doesn't speak Engrish as a third language who will actually help you.

      They're still better than LeadersHobby was, though. And I did hundreds of dollars of business with them in cheap motors; I think I may have single-handedly cleared out their Cali "Warehouse". ;)

      I make it a habit not to buy anything from them that I can't afford to eat the cost of; I've survived 2 returns with them, but thankfully, not on the same purchase like you. :p


      • Paul, honestly I thought about the same thing when I first heard of their name "Good Luck Buy". It always feels like "Good Luck with your purchase buddy":)) It is funny that they came up with this name...

        I have bought a few things from them and so far I have been in Good Luck:)

        • I was probably a bit overly harsh there; I've bought a LOT of stuff from them and only a couple incidents of goods that didn't meet expectations. Just the return process on those couple items really stuck in my mind. ;)

          Overall, I feel I've gotten good value from them, and will continue to buy there, for the same reasons as HobbyKing.


          • *Pokes thread*




            Okay... Just checking in. I won't have anymore news until I get a GPS/external compass here and can continue testing.


      • Paul

        Where is the best solder pad to add the Ceramic capacitor?

        Can I connect 5V and GND pad next to UART 2 ?



        • Naitsuga -

          My testing shows those pads to be a good low resistance (0.02Ω meas) connection to the +5V & GND pads at the regulator, so good for protecting the regulator. However, there's a bit of a longish trace between that point and the +5V rail at the ANALOG header (0.06Ω meas); it may not protect the CPU from resetting as well as a capacitor right across the pins on the bottom of the board at that +5V rail.

          This is where a bit of hands-on checking is in order; if your capacitor will fit inside the case on the underside of the PCB without shorting, I'd say better to solder right at the +5V rail at the A2 pin end of the Analog pin header; it has a 0.02Ω measured resistance with respect to the +5V IN at the USB. If soldering at the +5V & GND pin sockets right in front of the regulator on the top side will allow it to fit inside the case without shorting, then there will be better.

          EITHER location SHOULD work well; just the +5V rail at the A2 end is lower resistance overall, so in general better. In THEORY. However, definitely better to select a location where it will be protected by the case than to entertain the notion of running without the case.


  • Hi,  Weve had a pretty bad winter so I havent messed with my copters much this winter, I just found this thread and was a bit concerned because when I upgrade FW or download logs I bring the copter over and plug it into the usb while everything, radio modem, gps, rx, etc is still connected to the apm25's.

    I just tested the 2 apms I am using currently and found my 3.3v are reading 3.3v (I just checked off of the external compass power. so all is well.

    My question is, when I read "Attaching a radio receiver or MinimOSD to the APM while the APM is only powered through the USB (see video below)" from above it could be taken as not to plug in the rx, gps, etc.. AFTER or WHILE the APM is powered up by only the USB.  or does it mean to not use only USB power on an APM that has rx, GPS, etc... connected already?

    I guess for now, if I need to plug in I will just make sure I use a battery first then USB?

    thanks for any help,


    • I asked a similar question John.

      The answer is that using reliable power source (quality brand BEC or 3DR power module) with the USB is better. I was like you using only USB to do most of the programming because it is convenient. But from now on, I will always keep my flight battery attached so the APM should get the power both from USB and power module input.

      Hot plugings are definitely out. They do not recommend it. Watch Philip's videos. And if you must do these, then they recommend adding a 100uf ceramic capacitor to the Vcc rail ar the A2 servo input...

      See Philip's post a few pages back...

      • Alex,

        thanks, that's what I thought. I guess I got lucky.  I wonder if it is maybe poor power on the USB source that could be causing this problem. Just wondering cause I usually use high end motherboards and power supply in my PC, maybe this is why I got "Lucky" (good power from the USB)?

        thanks again, it is good to know. I did watch the videos and will continue reading/keeping up with this thread.


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