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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Replies to This Discussion

Thank you for the answers Randy. From what I gathered, regulator won't burn out for no reason. That was why I got worried. I thought it could burn out when a new firmware (at higher bus speed) is running.

I hope it won't happen to me. I handle my board properly but if it does, I will entertain Detlef's method before purchasing a new board.

@ Detlef, thank you for the post. It is great. 

Hi Alex,

From what I've read on the forums so far I only know Bruce who had a 3DR board with this defect. The rest is Chinese hardware and from those mostly Hobbyking which have this defect.

The datasheet rates the output to 100mA and "Continuous output current and operating junction temperature are limited by internal protection circuitry, but it is not recommended that the device operate under conditions beyond those specified in this table for extended periods of time."

So I think it needs real abuse to blow it -  a simple short probably won't kill it.

Hi Derlef!

Nice explanation,

Do you where the regulator is on a 2.5 board not 2.52.? Also do you know if it is an alternitive for the 2.5 , where to find it?

Thank you!

Hello Triantafillos,

I saw some pictures of the 2.5 board regulator over on rcgroups. It doesn't look very standard soldering iron friendly if that was the regulator in the picture.

Below the picture from rcgroups. I didn't look at the schematics of the 2.5 board but I would guess its the square lil chip on the bottom left (right picture)?

That sure would be a pain to replace with a regular soldering iron :(

Thank you Detlef!!

Yes you are right! I am going to order a new one, It can't be fixed from me!

Have nice flights!

Hi,

I have an APM2.5 (3DR) that intermittently suffers from the 'drunken HUD'. I observe this periodically if I leave it connected to MP while it is sitting on my desk. Needless to say it is useless in this state... I have measured the 3.3v output and it is a consistent 3.402V - 3.408V This is not too far off but still outside the spec for the regulator. Would you still suspect this as the cause? 

Hello James,

just a guess but if you have that issue with pre 3.1 software versions then I would say you have a different problem because with 3.0.1 it did not show for any of us even if you had the full 5V on the 3.3V supply.

If you only see it since you upgraded to 3.1 then hmmm maybeee? Maybe your meter is slightly off?

Great pic.

The APM2.5 regulator is the MIC5219-3.3YML TR.  It's $1.13 from digikey.

Well I just read this entire thread after experiencing the sane issues running 3.0.1 , I posted my issues last night and randy directed me here, I will be testing my voltage today and I will post my findings here.

OK, I just tested the voltage on the 2 outside pins of the external compass port and I'm getting 3.3 volts…… so my reg is good.

I installed the latest beta firmware 3.1 rc7 
But it seems I have a problem with GYRO too.

I have only used the 3drobotics power module 
so it us unlikely to have a burned regulator. 

 

any ideas ?

Edit: It is the authentic 3DRobotics APM board and not a clone.

Hi DSkoul, the reason for the blown 3.3V regulators has not been discovered yet but it really doesn't matter if you have used the 3DR power module or a BEC. You should measure if your 3.3V is really 3.3V to make sure! A 3DR power module does not protect you from a damaged 3.3V.

The only thing I've read out of all this is that it affects most the Chinese boards and less original 3DR boards. As far as Randy said 3DR has a quality check that tests the 3.3V during production so I would guess chances to get a bad 3DR board are slim. 

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