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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Thank you very much for checking that with your osci!

Looking at the stuff that is attached to the 100mA regulator - it should be no problem, even with the logging chip. I wonder why that problem is so epidemic. On the other hand there are several other commercial (partly with schematics or other infos) projects online that use 300mA+ reg for the job - or several regulators for sensors / cpu etc. So there is a lot of variations of the internal powersupply going on - but maybe there is a reason for them to use a way to big linear reg with 300mA+ for the job?

I'm not talking about a voltage problem , but a peak current , eg a "coil effect" on the board ,

what me say that is a current problem is that only "tps" are blown , "mic" absorb spikes larger current

Yes, sorry Alex, I should have made it clearer. This board is an RcT clone. I might add that I have a genuine 3DR 2.5 board and the reg. is working as it should.

you can easily repair by yourself and it will be cheaper than to return to diydrone

look here to know where you need soldering

2 solderings place are easy and one is smaller but if you take you time ,you will not have problem with it

it s the best way 

@jvmolo: Interesting, since RcT Arduflyer uses MIC5219 (3.3V 500mA)

You sure about that? The MIC uses a positive enable signal - means RCtimer must have changed the board layout and move pin 3 to the +5V. If you look at the board and see that pin 2&3 is connected to each other and GND then that excludes the use of the MIC.

My blown regulator board was a HK one and those use the negative enable. 

@chrashpilot, those shots were from the beginning when me and Bruce discovered the 3V3 issue. I haven't done any recent checking since my 2 boards work now with original TPSxx regulators.

@jcfa, since both those regulators have a current limiter integrated - I think - a sudden current spike must create a voltage drop. how else do you control current? And a constant overload would trigger a thermal shutdown, so I would exclude that as well.

I am pretty sure that if there is a reproducible issue with the TPS regulator 3DRs testing will uncover it.

Well I just downloaded the plans from the rtc timer site and picked out the part number. But I think there was some advertising going on some months ago where some clone manufacturer (RcT?) changed the powerdesign - maybe cloners found that issue earlier? - Don't know.

BTW here is the link to the board schematic I watched:

alors là titeuf tu fais tres fort :))

@ detlef : the solution is a voltage data logger on board on 3.3v line

Hmm good to know.

I have a RCt board currently in my quad. Don't know if its the one already with the MICxx. Looking at the eagle files they seem to have changed the layout. Looking at their website pictures they still post 2.5 board pictures and advertise it at 2.5.2. I guess keeping track of versions is not their strength :)

So far I had no luck with either clone. The first I got was the RCt with a defect flash and working regulator. My try to replace it with a HK clone ended that I got a board with a defect regulator.

Expect nothing and you won't be disappointed :)) 


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