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

    New video posted from Philip of how to replace the regulator and add the capacitor.  enjoy!

  • Developer

    I'm closing this thread.  One of the golden rules of diydrones is we try to treat each other with respect.  This thread seems to be a magnet for borderline (or over the line comments).  hopefully those who need help will find the info in the main area or the comments.  If not I'd recommend posting in the APM forum

  • Developer

    Let's all stay cool and on the topic of this thread.

  • Although I don't understand a word he says, his approach is very tidy. I will probably use this method with my next 3.3v reg replacement.

    • TIDY? Are you serious; that cobbled-together mess of wires and heat-shrink?

      Every place you add a solder joint is a point of failure. On top of that, there's no mechanical securing of the part; it's just dangling off the wires. AND it blocks BOTH UART0 AND the SPI bus.

      And on top of that, it's really just my mod in German; so somehow that makes it better? ;) :P


      *Not nearly funky enough*

      • Paul Krajewski,

        when I saw your solution when you posted the first time, I was encouraged to repair my APM that this arrest nearly a year. but I still had some doubts in welding where each leg of the component. the advantage is that this video leaves no doubt where solder each wire. My suggestion is that you put a picture showing exactly where each leg of welded component (the original photos could not identify without doubt) so people like me who do not speak English or German may give the due credits to his method
        excuse the mistakes and congratulation for the work

        • Ummm...

          I really don't understand what you're asking here; I do have it clearly marked in this photo:


          And also in this revised mod shown here:


          What it sounds like you're asking is that I spoon-feed you how to rebuild an APM. I'm not going to do that; and it isn't because I can't simplify this any more; it's because it would be DANGEROUS to do so.

          The bottom line is that this mod is laid out assuming that one has at least a fundamental understanding of electronics and how to assemble/solder components properly; it is intended as a guide for those who have that knowledge. It is NOT intended for those who have NO understanding of electronics at all; this is NOT like changing a light bulb in your car or replacing a fuse. It is important that you know what you are doing before attempting this Mod, or that you should take it to someone who DOES have a good understanding of electronics, for the same reason it's important to know why you don't just replace a blown 15A fuse with a 30A fuse.

          If you are looking for instructions like come with Legos, that's ENTIRELY inappropriate here; if you don't understand what you're doing with the Mod, then you likely don't understand the importance of keeping the modded APM out of regular service until you've tested it THOROUGHLY, and quite possibly don't even have a good understanding of how to test it thoroughly before putting it back in service either.

          I'm not going to help you, or anybody else, put an untested or improperly Modded APM in the air. I WILL show you how I THINK this Mod is best accomplished; you are welcome to take that knowledge to the technician of your choice if you don't feel you can do it yourself.


          There's a reason we don't give handguns to monkeys.

          • sorry for not having understood
            Monkey apologizes

      • WOW, forgive me Paul!

        Yep, it is your mod and it is in German, but for someone who is not all that great at soldering the small stuff, it may be an easier approach to it...English would be a bonus. I've replaced the regulator and added the 100uf capacitor in my APM2.5.2 and I can honestly say that my soldering hand was shaking as I was very worried about messing up something else in the process. Not being an electronics guru, which I'm willing to bet most in this hobby are not, I probably would have used this version of your mod as it seems a little less intimidating, maybe it's just because the mod is performed in the video which provides a bit of reassurance that your doing it correctly?  Although a dab of hot glue under the part would be a good idea.

        Just my opinion.


        BTW, I am grateful for this mod as it saved me from spending green on another board, thanks. 

        • But... but... but...

          The whole reason for the way I designed the mod was to make it easy to implement... that's WHY I located and marked the solder lands on the surrounding capacitors as the better place to solder to because they're bigger than the tiny pads on the board... heck, one of the solder points he uses is the same as the one I identified for 3.3V OUT. PLUS, with my setup, you don't lose ANY ports!

          And... and... and... Oh never mind. I give up. What chance does better engineering stand against a video on YoubTube and some guy with a foreign accent? A dash of heat shrink tubing and the deal is sealed... *rolleyes*


          I'll just be over here, crying in my liquid nitrogen...

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