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AC3.1 & blown 3.3V regulator (was AC3.1-rc5 SPI speed problem)

Posted by Randy on October 30, 2013 at 12:37am

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.

3691073724?profile=original

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Tags: accelerometer, batometer, spi, noise

Replies

  • Roy December 25, 2013 at 9:04am

    I still don't know what blows the regulators but for information I have changed the blown TPS79133 TWICE (or two times for our American cousins) and both the new and tested regs blew again with nothing other that a USB cable to the board.

    In the end I left the blown reg in place and soldered a 78L33 to the pads and the board now works geat. I doubt if I will use it on a bird but maybe I'll try it on a ground robot.

    Merry Xmas BTW :-)

  • Luc Maximilien December 25, 2013 at 5:36am

    I had the same issue with an APM 2.5 purchased at the end of March 2013 among other APM boards.

    I start to use that  board in September.

    With 3.01 the board was perfect , last 30 November , while updating trough Mission Planner, firmware from tri to quad , and probably from  3.01 to  3.1 . It just stop to work and shows no dataflash error, as described here :

    http://www.diydrones.com/forum/topics/apm-2-5-says-no-dataflash-ins...

    No more tension output from 3.3 volts regulator.

    I have change the regulator but the problem still there, no tension out  (??)

    Very disappointed with this issue.

    I 'm sure that the board failed during upgrade while connected with usb cable, nothing else connected,  almost unbelievable .

    This has destroy 90% of my confidence in 3DR product.

    And the answer of technical support received yesterday "is it possible for you to send a screenshot of this problem?" is not really encouraging...

  • Miguel Pereira December 24, 2013 at 1:49am

    Hi,

    Could it be possible that connecting the external magnetometer from the 3DR GPS + compass module, exceed the max current that the voltage regulator is able to deliver?

    I have a GPS + compass but untill now I'm just using the GPS part (using still the APM 2.5 internal compass).

    Miguel

  • Roy December 23, 2013 at 8:09pm

    I can confirm that removing the blown 3.3v reg and replacing it with a78L33 works very well!

  • Wolke December 22, 2013 at 4:46am

    hey,

    imo, my regulator is blown if i connect my ubec by mistake to the rc input side. but with right polarity. that is imo really strange. also i use a scorpion backup guard on a second output to prevent ubec failure. or can this be a problem. my first esc (motor1) is the one which power my apm. all other have un-stitched vcc wires. the scorpion backup guard is connected to pwm output  8. so pwm out 1is normally vcc in and pwm out 8 is backup guard.

    but if i do the mistake and connect my ubec(esc) to the rc input side from apm, no other componets or jacks was connected at the apm. i only was interested if the internal ubec from my esc1 works properly.

    /g

    wolke

    edit:

    i have a installed jumper 1

  • Alex O. December 21, 2013 at 7:04am

    Well this became more of an issue than I thought. I checked mine the first time I heard about this a few weeks ago. The reg. is fine. It shows 3.3 volts

    I haven't flown since then. The board (3DR APM 2.5) is currently loaded with 3.1-rc5. Plan on switching to 3.1 release version soon and start flying again.

    So all I want at this moment is for someone to tell me that I will be okay if I don't use JP1 and connect ESC backwards...

    I never use JP1 and all my ESCs are OPTO(no BECs in them). So there is no voltage going into the board. Even if I connect them backwards, it won't cause a problem. But I will not connect them backwards.  

    So Randy, can you say that mine will not blow by simply changing the software version?

     

    Also, I plan on switching to the external compass soon. Could that be a reason to blow a regulator?

  • Crashpilot1000 December 21, 2013 at 5:19am

    I don't find a warning sign/message/refund/repair initiative/further information in the shop.

    Is APM 2.0 affected as well ?

  • Developer
    Randy December 20, 2013 at 5:35pm

    I've updated the main intro area of this discussion to highlight the video and hopefully get people to the main answers they need quicker.

    Detlef (and others), please tell me if you think of some more details in the intro that would help.  Thanks for your help!

  • mP1 December 20, 2013 at 5:19pm

    I have a few 3DR APM but they are all 2.5. The other day i upgraded to 3.1 and got the bad health.

    I also perviously used to use a sonar but noticed it periodically got spikes in its height measurements. I have also cut the bridge to the internal compass. Im just wondering if my unreliability for the sonar(its not removed and in a box) was due to the bad 5v and not 3.3v ? DOes the sonar expect 3.3 ? I noticed in my logs the spikes from the sonar seemed to be sort of periodical, they were not really random and seemed to be equally spaced.

  • Reuben December 20, 2013 at 3:27pm

    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 ..plus the cost of the machine its self! 

    Cheers R

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