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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yes it should work perfectly, i was more curious about your preffered way of mounting the reg insides the case and wiring etc.. :)

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

If you live in the US I would go to Digikey, they ship USPS for low cost and the reg cost $0.40 per pcs. From Thailand takes forever to the US... I think I've ordered from that eBay seller before...

They also stock the original TPSxxx in the US...

78L33 is as bad as tps plus too high dropout (1.7v)

I could understand your big soldering iron reason for the use of the 1A reg but its definitely way oversize :))

I measure my entire systems current consumption with APM2.5.2, GPS., RX, ext compass, and minimOSD slightly over 100mA. What for do you need 1A on the 3.3V side and why would a 100mA for 3.3V not be enough? I don't believe this overload scenario in this case as reason to break the regulator.

So no picture or anything Roy?

you are right for the continuous current but maybe that there is current peaks , at boot

maybe this where the problem , dataflash is also supplied by 3.3v

This is the best I can produce with an iphone and photoshop at short notice. :-)

Hope it will do.

Soldered with an Antex 25W iron (hence the mess)

The big black blob is 1/4" double sided servo tape.

Thanks Roy. I am looking at your picture and compare it to the two pictures on top of this page and the board you have looks like the on the left which is APM 2.5.2 not the APM 2.5 on the right.

Please correct me if I am wrong but the difficulty is to do this kind of replacement on the boards like the one on the right picture.

Detlef, you may chime in too. Am I mistaken?

Thanks for your effort again Roy...

There is no voltage break in at boot or power up time, check my earlier post here:

That's a oscilloscope screenshot of the 5V USB and 3.3V after regulator replacement. My 5V had much more a problem while 3.3V come up nice and clean. Also later it did not dip on the 3.3V level. So to me the TPSxx or 78L33 both are fully sufficient in size.

There is probably an easy way to blow the TPSxxx otherwise there would not be so many ppl having a bad one now but under normal conditions I would say its pretty safe to survive.

Didn't find the eagle files but here is a picture to explain how I meant it. The 2.5 board (forgive me the RCTimer image - was all I could find for 2.5 that quick) has all voltages on the pin rail. +5V, GND, and 3.3V. Just knock off the defect SMD regulator and solder a new one to those pads. I am sure you'll find a spot where it can lay flat on the board (top side) maybe with some tape/glue.

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!



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