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

    It's slightly off topic but I found a board that had the "No Dataflash inserted" message and it produced 0V when I tested the 3.3V regulator according to the video.  When I looked closely at the board I found that a resistor was missing right near the 3.3V regulator.  The board was being used by a local University here in Japan so I'm not sure if they banged it around a bit or not but in any case, 3DR has already processed the RMA.


  • Were can i buy these chips?
  • I have several APMs half 3DR ,half not clones but rather other manufacturers and I have had plenty of flights and plenty of plugging unplugging ..crashes and crossed wires .. I have never had an issue yet with any of them .. It has been suggested that when plugging in the main battery you get a huge spark while it charges the caps on the ESC's and this spark could have adverse effects ..yet to be proven though...

    I would also like to thank the Whole TEAM ..for all great work and giving us all something to play with ..  

    Regards R

  • I have a proposed fix for the APM2.5.x 3.3V regulator issues here

    Texas Instruments is the only manufacturer, we are all in the same boat with this issue.

    It has to do with the 5V input suddenly going down to 0V which applies -3.3V across the 3.3V regulator which is only rated to -0.3V Absolute maximum.

    It has nothing to do with how you power the APM with any UBEC.

    A loose 5V supply connection I suspect could trigger the scenario which damages the 3.3V regulator, anything that shorts out the 5V will also likely trigger the damage.

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  • Has any progress been made to determine the root cause of the blown 3.3V regulators?


  • Hi,

    Does anyone know cheap alternative to buy TPS79133DBVR? from Digi-key shipping to Brazil is US$ 40


  • Alex, Randy,

    Thanks again.  At this point I think I will wait out the Pixhawk and uBlox GPS/compass combo.  However, I will keep the APM 2.5.2 for a rainy day project. 

    Are there any projects for the APM that do NOT require a GPS?  I can't think of any.


  • All,

    It now appears that I have lost my uBlox GPS module after transplanting the 3.3v regulator.  It no longer powers up.  Is there a possibility that I could have damaged the board while soldering on the new regulator?

    I have log files but I don't know what I should be looking for.  I have tested both GPS ports.  When I do a CLI based test of the GPS all I get in return are "................................" with no data.

    At least my HUD has stopped wobbling.



  • I have successfully replace the 3.3V regulator in my original APM 2.5 that got a "no dataflash error" while connected only with usb cable .

    Soldering was quite simple removing the faulty component,  a bit more  difficult.

    I put a drop of tin solder that touch the three pins while lifting  the side of the regulator with a thin blade (it must be thin to not cool the tin solder  drop) and repeat the same on the other two pins.

    I use tin-lead solder because of lower temperature needed.

  • I also have the same voltage regulator casualty but without a 3.3V output - bought the APM 2.5.2 board from China.

    The APM is being powered by an ESC (at the APM input, only 5V & GND connected to the board from ESC). We got the board to work with our setup initially, got it to arm/disarm with the motors. But in some kind of simultaneous combination with the input voltage, with the USB connected/disconnected and/or APM board powered on – all of a sudden, we couldn’t get connected to Mavlink. I did some troubleshooting and found that the voltage regulator did not have a 3.3V output.

    Also, I’ve noticed that if the USB is connected to the board, with no battery connected, it seemed like the USB is making/breaking when we just toggle the BEC power connection to the APM. The PC gives a sound alert that the USB port comes and goes. Weird.

    I'm going to replace the part this week and repeat our setup. Still need to figure out the root cause for such failure to prevent it to happen again.

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