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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            • wooow... looks safe now!! I guess you can hot-plug now everything and anything while you are flying LOL Sorry, couldn't resist to comment...

              I think its time for your to get in the air with that thing... otherwise you continue to make a whole new animal out of it :))))

              • LOL...

                That's what I meant by buffer caps at ANY plug-in header. Anyplace where your filters are on the other side of a plug is a bad thing, as is anyplace where there's a long trace between a power plug and your filters. These are things they taught me in Fundamentals of Circuit Design when I went to school; but I imagine things are different now, what with most everything being digital. For my own use, I tend to prefer to over-engineer, build a tank and fugggeddaboudddittt.

                I have a case, power module and cheap GPS coming on the slow boat from China; I'll probably do the jD IO board so it can talk to my FRSKy Telemetry, too.

                I have a 235mm MicroQuad frame that can carry this thing; I may take a little detour down that road if I run out of stuff to build on my Cub while I wait.


                • Oh, now y'all are just pokin' fun at me. :p

                  It's okay, I know I'm hopelessly analog; I learned electronics when multi-layer PCBs were a relatively recent development and I still had to do service on tube TVs.

                  But I still understand why buffer caps are a good thing; it's not the times when everything works RIGHT that they're a good idea; it's when things go WRONG... like Joe's son's doing crash-testing with his quad... that they can save yer bacon. That's why I put them at all the rails, not just the one we're having a problem with today.

                  You never know when or where something is going to get unplugged in a crash, or where corrosion will strike... THAT is the reason it's most important to have something that's SOLDERED in place, not like a plug-in "brownout stopper" cap.

                  Yeah, maybe I'm being paranoid; a bit silly even. but as you say, now I can even hot-plug while it's flying; so maybe that will give the gremlins a bit more to gnaw on before they bring my beast down. ;)


                  I miss living in a world where the Beatles could happen...

                  • Ok, no more questions your honor - I see you are fully equipped!! LOL nice shot...

                  • Wow... I am jealous of your high-tech optical tools:)

                  • Detlef -


                    I have no idea what you're talking about... "optical magnification gadgets"... ;-P


                  • ahhh now I understand why you use that big regulator... hahaha you have the same issues like me that we can barely see those tiny legs of the original regulator without all those optical magnification gadgets... LOL

                    I liked those times when it was still worth fixing a TV! Today you don't find anyone who can fix it anymore and if then you couldn't pay him without getting for the same money 3 TVs...

                • said.

  • Nice work! 

    The main article could do with a little more clarification of problem, cause, and solution though imho.

  • You forgot the fact that the buffer just above the regulator is wrongly wired and can provoque some issues like short circuit on 3v3 ! And could be revealed by intensive use of log in flash memory.


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