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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  • Hi guys, I would like to thank everyone for all the work done. What a dedicated group! This will be my first post, I've spent several months reading, ordering parts and building. I am building a Hex using the RCtimer 2.5.2 board. I have followed all the instructions, Especially Jabram's posts. ESC's are not powering the board a separate 5v reg does that. 3DR 413mhz radio for telemetry, connects to Mission Planner just fine. Black foam on the barometer. Turnigy ESC's I flashed with SimonK. It hovers good. GPS locks in, But, that is about as far as I have got, wind, weather hasn't allowed any other testing and tuning. The hud was very stable.

    Today, I upgraded the firmware to 3.1 and as soon as it booted, Mission planner shows and speaks "Bad Gyro Health" and some other message that sounds like: "prettier ends not healthy" can't really understand what the first word is.

    Am I one of the unfortunates with a blown 3.3. Regulator? I measured it and it's 4.7v or so. And, if so, what is the recommended replacement? If I replace it, will the board work or does the excess voltage blow anything else? I can do the repair as long as I get the proper part and nothing else is blown. I read about this being a problem with the bus speed increase. I haven't tried it but if I go back to the previous firmware is it possible it might work since the bus will run slower?  Any thoughts or replies would be greatly appreciated. 

  • Distributor

    Hi guys,

    A client of mine just sent me back a damaged jDrones' APM board, problem description: "BAD GYRO message on HUD"
    It means the problem is not only regarding to 3DR boards, right?

  • I had the same problem as most, tested my voltage and it was ~5v instead of 3.3v. Ordered the part from digijey and replaced it and all works fine now. No issues and an easy fix.
  • Well I just read this entire thread after experiencing the sane issues running 3.0.1 , I posted my issues last night and randy directed me here, I will be testing my voltage today and I will post my findings here.
  • Hi,

    I have an APM2.5 (3DR) that intermittently suffers from the 'drunken HUD'. I observe this periodically if I leave it connected to MP while it is sitting on my desk. Needless to say it is useless in this state... I have measured the 3.3v output and it is a consistent 3.402V - 3.408V This is not too far off but still outside the spec for the regulator. Would you still suspect this as the cause? 

  • Developer

    Alex O asked:

    -Does this affect certain batch of APM2.5s or it could happen to anyone?

    I asked Craig (3dr) and he tells me that they specifically check this when the boards leave the factory.  All humans make mistakes but as far as I know, there is no know batch of APMs that left the factory with this problem.

    -If so, what can we DO to prevent this from happening?

    I've personally never had this problem so I think if you handle your boards carefully you don't need to worry.  In particular don't hitch up your ESCs backwards with the JP1 jumper in place.  There may be other ways to cause this that I don't know about though.

    -And lastly, if it does happen, what are our options?

    We're trying to make AC3.1 automatically downgrade the SPI bus speed so if you have the problem you'll get a warning on the HUD and you'll need to disable one of the ARMING_CHECKs but the copter should still fly as well as it did with AC3.0.1.  That downgrading code is in -rc7 but it's not working so it needs to be revisited.

    Of course, the incorrect voltage is possibly already causing small glitches even with AC3.0.1 so the best solution is a new board or to replace the regulator.  Detlef's managed that, I personally don't actually know where the regulator is on the board nor exactly where to get a replacement regulator...but I'm hopeful we those details will emerge!

  • Detlef, how were you powering the APM? On the input side?

  • Developer

    I've made a little video of how someone could test the regulator on an APM2.6 without pulling it from it's case.  Of course as mentioned earlier in this thread there are a number of places it can be tested, this is just one of them.

  • Hmm while I was testing last night power supplies on the fixed board I noticed that my internal compass is behaving kind of odd. It doesn't seem to point into the right direction and it starts drifting if you let the board sit for a while. Also my HUD slightly moves now and does not sit still as it did before with the external compass when I used it in the quadcopter.

    Can that be caused by a faulty magnetometer or are movements in the HUD solely based on gyro and/or accelerometer??

    I just ordered another external compass for testing but I almost suspect that the internal compass didn't like the 5V on the 3.3V supply?

  • Ok thanks Detlef, back to square one.

This reply was deleted.


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