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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  • Randy, et al,

    I too believe I have blown out my 3.3 volt regulator.  After upgrading AC 3.1 from 3.0.1 on my APM 2.5, I immediately noticed the choppy HUD as well as gyro not healthy alerts.  Upon testing the IC2 port I did notice 4.9 volts rather than 3.3.  To my knowledge, I do NOT have a PPM encoder unless it is internal to the APM 2.5.  I know I do not have an external PPM encoder similar to the unit being offered with the PixHawk.

    That said, I have ordered the correct regulator from Digi-Key as well as treated myself to a shiny new (backordered) PixHawk and GPS+ Mag combo.  I did not order the PPM encoder because I use a Spektrum AR8000 Rx (is that okay?).  In the event that I cannot successfully replace the regulator what is a gyro-less APM 2.5 still good for? AruduRover?

    Could someone that has successfully replaced their own 3.3 volt regulator please post a detailed (w/ pics) best practices step-by-step of the procedure that would be greatly appreciated!

    Thank you in advance, and Happy New Year!


  • I wonder how many of you with blown 3.3V regulator  did update of PPm encoder, maybe that's connection....I am no expert this just came to my mind and I share it.... 

  • Can we send our APMs in to be repaired or replaced? This seems to be a common problem. I'm still waiting for my PixHawk and now I find out my APM won't work with 3.1 because of this gyro error. =[  Frustrated!

  • if anyone is interested in buying some 78L33 regs cheap, here they are:

  • I have an old APM 2.5  running 3.1 that suffers from the crazy HUD and is absolutely impossible to just flips over as soon as you give it throttle.  I tested the voltage and I am getting the correct 3.3v and not the 5v being discussed.  Could there be another culprit somewhere?  I would love to figure out what it is so that I can use the APM again.

  • Hello guys,

    my friend has the crazy HUD problem with APM2.5.

    could you please point us to a hardware based solution (replacing the regulator) info?

    how to solder? which regulator to get?

    perhaps we can replace the tiny reg with a larger one jumpered to the right spots?

    also, will running an older version (i.e 3.0.1) with the sensors at 5V cause the sensors to eventually fail from the higher voltage?

  • Can anyone tell me what the pin hole next to 'U2' (circled in green in pic below) is for/ connected to?  I've looked for schematics/circuit diagram but not found anything showing these pins.


    I had a blown 3.3v reg on a clone board - only symptom was problems after performing compass calibration on an external compass.  Replaced with a Micrel MIC5205-3.3YM5 with positive enable so jumpered across to this point.  3.3v is ok now and compass works ok but GPS is considerably worse than before with high HDOP and massive position jumps in MP.  Could be coincidental but I would like to check I haven't affected the GPS by connecting to the point circled in the picture.

    If you can get the TPS79133DBVR I would definately recommend using it above the MIC5205-3.3YM5 since the enable pin is correct logic for the board and from datasheets it appears it should have lower noise when used with the existing on-board capacitors.

  • I know next to nothing about electronic design, therefore laugh if you must. If the regulator is supposed to provide a nice 3.3v to various sensors why is it possible for 5v to make it to these devices ? Shouldnt a blow regular kill all power to the other side of the circuit ?

  • Where are the Aussies here buying their replacement regulators ?

  • Am wondering if the USB could be a common link among those who have alot of blown regs?

    Dirty 5v from their PC?

    Can I get some advice on whether this will work for 3.3v supply? Might as well go heavy duty...

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