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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see specs mic 5219 and specs tps

Hi guys,

A client of mine just sent me back a damaged jDrones' APM board, problem description: "BAD GYRO message on HUD"
It means the problem is not only regarding to 3DR boards, right?

Hello, Detlef

Thanks for the quick reply.
I have incorporated a lot of APm for customers, so far I have still no reports of broken boards.
the problem is known, I think it will be fixed in the next version.
It would be nice to find a way to identify the error before it comes to a crash.
I have a board which determines about 50 hours flight time. without any problems.



Hi Rainer,

I think you will be safe in the future too. This is not a general problem and its not caused by the new firmware with the increases SPI bus speed. The new 8MHz only make that defect 3.3V regulator visible. If you read the previous posts here, 3DR has a quality check that verifies the 3.3V before their boards leave the factory.

My board for example came directly defect from my Chinese supplier as it had  startup problems since new (also an indication for the defect 3.3V).

The used TICxxx has a current limiter built in and is rated at 100mA. The MICxxx might be a littler stronger but it only does 500mA peak and not continuous (~150-200mA). Rule of thumb the higher the input voltage the lower the continuous current you can use. Since you cant beat physics a linear regulator has to basically burn the voltage that it cuts at any given current. So TIC and MIC both convert the cut 1.7V mupliplied by the drawn current in Watt or heat and the size of the component and material only allows for so much heat to be transferred before it reaches the critical temperature that destroys the component.

Anyway, I replaced mine with an identical TICxxx and my previous defect board works without problems. I even use an external compass on the board that adds to the load on the 3.3V. It sits now in a Bixler and its flying since ...

That 3.3V regulator is probably easier to destroy but I doubt that it dies just by normal use as both my APM boards sit in the same environment as the broken one before and both boards work now.

I wouldn't get to worried about it...

Hi guys, I would like to thank everyone for all the work done. What a dedicated group! This will be my first post, I've spent several months reading, ordering parts and building. I am building a Hex using the RCtimer 2.5.2 board. I have followed all the instructions, Especially Jabram's posts. ESC's are not powering the board a separate 5v reg does that. 3DR 413mhz radio for telemetry, connects to Mission Planner just fine. Black foam on the barometer. Turnigy ESC's I flashed with SimonK. It hovers good. GPS locks in, But, that is about as far as I have got, wind, weather hasn't allowed any other testing and tuning. The hud was very stable.

Today, I upgraded the firmware to 3.1 and as soon as it booted, Mission planner shows and speaks "Bad Gyro Health" and some other message that sounds like: "prettier ends not healthy" can't really understand what the first word is.

Am I one of the unfortunates with a blown 3.3. Regulator? I measured it and it's 4.7v or so. And, if so, what is the recommended replacement? If I replace it, will the board work or does the excess voltage blow anything else? I can do the repair as long as I get the proper part and nothing else is blown. I read about this being a problem with the bus speed increase. I haven't tried it but if I go back to the previous firmware is it possible it might work since the bus will run slower?  Any thoughts or replies would be greatly appreciated. 

Hello Kelly, I can only speak for my case. A HK 2.5.2 board with a defect since new. Yes it did work every time I went back to a FW version with the slower SPI speed and was only acting up with FW3.1 and betas that used the 8MHz speed.

It also survived the high voltage on the 3.3V supply as I have fixed the board by replacing the regulator as described in previous posts. Nothing else was damaged to the non usable extend. If my 3.3V components got any pre-damage or stress that will show later?? Maybe!!

I put the original TIC xxx back on mine. There is a MIC xxx that lists slightly higher specs for current (which would be nice) and much higher allowable input voltages (which is not really needed)

good luck with yours... if you attempt to fix it :)

Thanks for the reply Detlef, I think I will try to go back to 3.0.1 and see if it works. If not, I guess the regulator is really blown and needs replaced. After you fixed yours, are you running 3.1? I don't want to replace it, then blow it again with 3.1 Maybe running the bus so much faster must increase the current draw of the accel, baro and mag and the regulator fails since it's only designed for 100ma? I didn't know HK sold an identical board as the RCTimer one. Just checked, they look nearly identical. I'll go back and read this post from the beginning and see what I can find out about all this. Thanks again!

Do you have DigiKey numbers handy for both regulator components?

Hi . I have been reading the post regarding the 3.3v issue ..What I want to know is .. 

a) What is causing it to blow (short out) ? Software or too much load?

b) If it is replaced will it blow again ?

c) What model of Reg should we use .. a higher rated one?

 As I only see posting for Micxxx  no numbers.

 Now I am too scared to fly as I have thousands of $$  hanging under my copter the cost of the machine its self! 

Cheers R

Detlef, never mind providing the part numbers, read through this post and found them. I just reverted back to 3.0.1 and the Hud is stable again. I guess at least I can practice hovering again. For quite some time I've noticed the VSI seemed to jump around even sitting. I have the black dense foam and a bright flashlight wouldn't affect it. Mabye the Regulator was already blown, I guess I will never know.  I do remember early on checking my 3.3v per a Jabram post and it was good. But after reverting back, It's still 4.78 so, the regulator has released the "magic smoke" Going to order a couple and replace it with a spare to replace it if 3.2 kills it again. It's at least big enough I can see it so I'm confident I can replace it. What a crazy hobby! I'll post my findings back in a week or two. 



     That's right.  The blown regulator can happen to the APM2.x boards and any of the clones.

I think the symptoms slightly differ and also in strength. With 3.0.1 mine flew perfectly but the board with blown regulator had issues to boot correctly if I power all together - even with 3.0.1. I had to power ESC and RX first and a little delayed power the APM or it would never boot. It did that since I got it new from HK. With the regulator fixed its gone - no more special power-up procedures.

Yes with the fixed regulator its working with 3.1,  any of the beta versions and also the final version. I used the original part number as posted here: a stronger version should be this one: MIC5219

I wouldn't recommend to continue flying with the 5V on the 3.3V side. Its only stressing the sensors with over-voltage and maybe cause some permanent damage.

Overall I would say its definitely not the software that blows the regulator. The new software only shows a effects of a blown regulator because the higher bus speed causes overpowered sensors to act up.

Thanks again, just ordered the parts and, taking your advise, will let it sit until I get it fixed. Plenty of other RC projects to work on. 


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