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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      • Thanks for taking care of that. I try to stay in the topic as much as possible but sometimes we all get a bit off track...

        • no no no... shoot him... I am pretty sure he was already thinking about pricing LOL

          • I see you trying to get me in trouble here... It ain't gonna work.

            And remember we need to stay in topic. If I get another warning, I will point you as the responsible:)))

            • hahaha... ok blame me, some more humor since everyone is getting a little tense here :)

              • Developer
                Lol :). Yes, less tension is good :)
  • Emin, relax, please.  Jumping to conclusions is not helpful.

  • I think this entire thread and issue only applies to APM 2.5.2 and APM 2.6 boards which use the TPS79133DBVR regulator. All other boards like Pixhawk, PX4, and even APM2.5 use different ways and regulators to create the 3.3V and are not affected by this - or am I mistaken?

    I was doing yesterday a hot-plug test on my APM while on battery power with 3DR power module plugging my minimOSD at least 20 times in and out while on power and nothing happened (EDIT: no capacitor installed). Same procedure done on my laptop USB power (no battery) and it created the deadly voltage sag for the TPS79133DBVR to hang up and kill itself at least 1 out of 5 times.

    Nobody needs to get paranoid that all other boards are now affected and if you follow some simple rules your APM 2.5.2 and 2.6 are safe as well.

    I further think that there is no difference in clone or original - the 3.3V regulators on those both die the same way if mistreated. There is nothing better on one or the other. But I do believe that the Chinese clones ship more defect boards out than 3DR does and they do not notice it at least on those where the 3.3V goes to 5V because the clones I've gotten all had older firmware (2.9x) on it which does not expose the 5V on 3.3V.

    It has its flaws but to me the APM design overall has proven how stable it works and doesn't quit in mid air hardware wise.

    • Developer
      @detlef. You are correct, just the ones fitted with the TPS.

      Many are arriving DOA from some Chinese vendors. But that is not the discussion here.

      @ Emin.... This thread is not to discuss pricing, that is a matter for each company, and not a topic for this thread.

      Please only comment on constructive issues that are on topic
  • No we need to make us not worry.
    errors you have in your car because you're doing you.
    also no worries.
    I have installed some Pixhawks running properly.
    The 20 built-in APM also run without problems

  • Hi there,
    No it did not blow WHEN i plugged it in, it was ALREADY in and working with all bits plugged in on an earlier version of the firmware. It stopped working WHEN I upgraded the firmware, and now only works WHEN I pull the compass out.
This reply was deleted.


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