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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  • Thankfully DigiKey Canada had stock so I ordered 5 units (spares for future stupidity on my part ...) and should be here tomorrow.

    Randy I understand, not shooting the messenger.  Been through this rodeo before with my day job.   Had hardware that has worked for 4 years all of sudden start failing like mad in the field... devs bumped up a few clocks and multipliers to resolve another issue which stressed out old under spec'd components.  Huge shouting match between hardware Eng's and Programmers... who then of course brought marketing and purchasing in on it for trying to save money years ago by using cheaper components...etc etc etc.   Not saying this is what happened in this case but I feel for you.

    However mine was good at 3.3v before I upgraded.   Flew perfect with 2.9x.  Tested by removing the I2C connector from the 3DR external compass but left everything else plugged in.  Connected USB power, measured 3.3v and then removed USB and plugged I2C back into compass.

    Then connected entire quad to USB port and upgraded to 3.1.2 successfully but right after could not connect via Mavlink (Mission Planner).   Terminal Window worked just fine.  After many hours of pulling hair out, finally re-checked 3.3v and found it was 0v.

    During this time I had not unplugged anything while USB or battery connected.  Hence why I'm concerned this may happen again.

    Is the 3.3v rail data logged anywhere in the APM so we can keep an eye on it?


    This does bring up a good point however, will there be an APM 2.7 that is beefed up to handle all kinds of "user error" (as out lined in this thread where people are adding caps etc) or should we move to the Pixhawk?

    I haven't looked at the Pixhawk yet as usually the first rev or two of a design is full of PCB layout flaws etc so I typically wait for a few versions in.   Don't even know yet if my external 3DR compass/GPS from my APM 2.6 will work with it.



    • There won't be APM 2.7. That's the reason they moved to Pixhawk and PX4. APM 2.x series maxed out the CPU usage already. So they needed something with more powerful CPU thus the Pixhawk series...

      As far as I know all the external units that work for APM 2.x can be used on Pixhawk as well...

      • Developer
        @alex O

        Who says?
        • @ Philip

          "Who says?"

          I didn't understand!.. Which of my comment(s) does it refer to?

          • A guess this one:

            There won't be APM 2.7

            • I see it... It would surprise me if I see APM 2.7 but I wouldn't be sad at all. Since the CPU is maxed out and they moved to higher end units and the development is mostly working on Pixhawk/PX4 hardware from now on, the logical conclusion for me to believe that there wouldn't be a later development after APM 2.6. But at the same time this 3.3 regulator issue wore out the APM's reputation. So I wouldn't blame them if they want to clear that up with APM 2.7 

              Let's see if there would be one... 

              • Personally, I feel it would be a foolish move to abandon the APM platform; not all of us are trying to build uber-quadcopter-droids that need all that massive CPU power and the cost that comes with it. We're getting to the point in that market where Intel product is starting to look attractive. ;)

                I, for one, will likely never use all the power the 2.5.2 has on tap as long as it's in a plane... so why would want to have ONLY the option of an even bigger, more expensive FC for the piddly little bit I'm doing with it?

                This would likely drive away users to the Multi-Wii platform; their GUI isn't as robust or user-friendly as MP (IMHO); but as many have noted, the genuine 3DR FC product is pretty pricey and they NEED an "Entry-Level" or "Discount Market" product or they will be overwhelmed by the "Zergling Rush" of people passing them up for a platform that can  satisfy their "Just Starting Out" needs at a fifth the price.

                The PixHawk is going toe-to-toe with the Naza; that's great for those who want only the best. The rest of us need a more basic platform and ARE willing to spend more for 3DR quality; we just can't spend THAT much more. Turning the APM platform into an "Entry-Level" product and discounting it a LITTLE would be a wise marketing strategy.

                Look at it this way... I've done the Electronics Retail (AND Electronics Resale) market myself. I learned quickly that you have to have BOTH High-End AND Low-End product ON HAND for immediate sale. The High-End product is what you pay lots of attention to and make it look spiffy with the latest gadgetry and displays; it is where you make your profit.

                The Low-End product is what you make sure just plain works and employ the KISS principle; you keep plenty on hand and you streamline the buying process with simple a la carte AND bundle pricing. You spend your time there making it easy to BUY because your profit margin is smaller and because in the end, THAT product is what keeps the doors open.

                Even APPLE has had to ultimately kneel down and pray before the altar of "What Sells"; THIS is the reality of selling Tech in the modern marketplace.


                *NOT pound-foolish*

      • Developer

        My understanding is that there is a modification to the APM2.6 coming to help protect against the failure case that Philip has found (i.e plugging in the radio while the board is powered through the USB).  Until then I guess there is this cap fix that Philip has found.

      • Hi,

        As far as I know, the old external compass will not work on Pixhawk. I know the external compas/GPS combo do work on Pixhawk.


        • You could be correct Xerravon. I remember seeing a similar note on external mag. page. But since Tim has APM 2.6, it won't matter for him. He has the GPS/Compass combo...

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