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.

For 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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Randy, is it possible that you got the wrong firmware linked? If I load that it comes back as ArduRover v2.43?

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?


     It's certainly possible that the compass was damaged although I've never heard of that.

     the HUD will also move because of the centrifugal force correction based upon the GPS velocity.  It's especially noticeable if the GPS position/velocity is not good (like when you're indoors) and when you're armed.  When you're disarmed it turns that off so it should be perfectly still.

     the compass will affect the heading but it shouldn't make the HUD move up and down.


    Jeepers, you're right!  sorry.  I've deleted that firmware.  -rc7 has the fix in it but it doesn't seem to work.  I've got Bruce's old board now so I can look at it more closely and see if a software fix is possible.

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.

Thanks Randy once again!

My regulator is blown.....  You were, on the 3.3v out is 4,86...

I am going for a new one.

I think I will have a closer look at that again. Was late that night moving FW from plane to rover and copter :)

I have to re-check under what conditions it moves. When I say move it was by far not as bad as with the 5V on the 3.3V but you can see that its not sitting completely still.

Since I used it before with an external compass I couldn't say how it was acting before and the external compass hat a 3-5V range - so that didn't care about 5V supply.

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

I have powered mine over the output rail with a switch over JP1. That way I could power up all periphery and then delayed flip the switch to turn on the APM but now I don't need that no more.

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!

Just got familiar with this issue from the "Arducopter 3.0.1 released!" thread. I have a few questions if you wouldn't mind. My apologies if these have been answered previously...

I just checked mine since I recently went to 3.1 from 3.0

Mine works fine: 3.3volts at the I2C:)

But now I have some questions:

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

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

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

Many thanks...

Hi Randy, I replied to your question earlier and posted a short description here in this thread.


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