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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    Ok, so the problem appears to actually be that I'm good at making up stories but really bad at counting.  I've looked again closely at my GPS cable with the white ends and, like yours, it's 6pins on both ends.  really sorry about the confusion.  Here's the diagram again.

No Problem Randy. I am glad we agreed on the pin count:)

But do you also have the answer why the Ground (GND) is on the Red wire side and VCC is on the Black side?

This is so confusing? Is this intentional or just some missassmebly on those harnesses?

Michael, I never used one but as far as I heard from others, I wouldn't buy the MediaTek GPS unit. It is not as accurate as the uBlox one. Stay with uBlox

About those after market units, I guess if the price difference is a lot, it may be worth the shot. I never tried one myself but if I find one at a very good price, I would try it...


     My guess is that the hardware guys just overlooked that detail.  I imagine when they buy the cables from the supplier they always come with the red cable on the edge..thinking that the user would be using a device that conforms to the standard of always having VCC on that edge...but sadly the APM2 doesn't conform.  3dr could probably have ordered special cables but they didn't..i imagine because they were concentrating on the next big thing.

I would guess the red wire only indicates pin #1 in those cables as like in those flat ribbon computer cables. Doesn't necessarily mean that it is Vcc or + on its side or pin.

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.


You can fly it in stabilize, altitude hold, simple mode and obviously manual mode. 

I would try the GPS you have on another board just to make sure it is not the problem. But I would hesitate to connect another GPS to your APM board just in case there is something shorting at the GPS port that causes the GPS to fail.

Good luck with Pixhawk. I am will buy me one of those in the future...

Well 3DR has a long history of power hardwarefails if that story is just half true: I guess we will see some paid off sweet talk about the next issues that are already in the pipeline.

What a bunch of bullcrap.  Written by somebody who clearly has no idea what he's talking about, or how this program runs.  Sounds like sour grapes to me from another one of the OS UAV projects who can't figure out how to fly as well as us.

I've seen these sorts of comments so many times, and they are NEVER substantiated by any particular example of code that was "stolen". If it's as rampant as they suggest, it should be easy to find something.  Anything.

I agree with them 100 percent to


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


This is where I got mine. Took less than 2 weeks to Uk


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