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.
Replies
It's a fair question if you don't know me well.
No, I didn't make the change to mess over the clone boards, we just needed the extra CPU to make telemetry work while in Loiter modes and also fix the alt hold problems on the octa's. I spent days trying to come up with a way to detect and revert the bus speed but I couldn't get it to work reliably.
Emin, now you are slow... I was just joking about Randy's program change :)
Do you really believe what you are writing now?
I would say if the clones would be real clones of the original then the 3.3V regulator would be working, wouldn't it?
it is still possible,its not Randys fault if 3DR ask him to do something...
Is a voltage reading of 3.5V on that 3.3V line indicative of a blown regulator? I'm troubleshooting for a friend and found the recent post on just removing the regulator and powering it externally from a 3.3V source. I figured why not since it's basically dead as is. This is a clone board so no big deal if it but I'm curious if that might be why there have been issues on his board.
However, double check the voltage, it should be right on 3.3....
Is this the voltage before or after the mod?
Hello, I have been playing with a APM 2.5.2 board with a blown up regulator. I was able to remove and replace the small smd regulator. The voltage after the repair when measured at the 12c port was still approx. 4.7 volts. I thought it was a bad regulator, so I tried two more times. I got the same readings.
I now am fooling with a larger regulator just to make it easier to try different things. I tapped into 5v and ground on one of the open side rails and verified the voltage out of the regulator is at
3.29 volts.
My issue is when I connect the 3.3 lead to the board, the voltage at the 12c port measures 4.73?? The voltage going into the board from the USB is 4.97. It effectively dropped the voltage to the sensors .24v.
I then connected the regulator 3.3 lead to the backside of the 12c connector. Same readings. Where is the extra voltage coming from?? Is there a burned out diode or something. I am lost at this point.
I also noticed there is 4.97v at the 12c port with the regulator completely removed?
I wonder if the 5v is coming from the dataflash level translator. There is a Vcca for the A side of the chip that is tied to that 3v3 rail but due to a board layout issue, 5v is being applied to the data lines on the A side when 3.3v is expected. I wonder if the 5v is bleeding through? I can't imagine the currents being very high though. It may be worthwhile for you to cut the Vcca and Vccb lines of that chip. The worst that will happen by doing this is that you will lose dataflash logging capabilities. Check Guaifi's post to figure out how. I consider this a last resort option though. I am also certain that the translator chip is not the root cause of 3.3v reg failures.
Just to confirm. no.... This issue has been thoughtfully considered, the VCCA and VCCB ARE correctly powered. it is the data-lines that are backwards NOT the power.
As the Dataflash is 5v tolerant, this is not the issue. there has been a LOT of investigation into this potential, but it is not the cause.
The main evidence for this, is actually the number of boards out there. if this were the cause,
1. it would affect the 3DR boards just as much as the clones.
2. replacing the reg would not fix it.
DO NOT cut those lines. if you have the 3.3v issue, my suggestion is to contact your supplier. if it is a 3DR board, let 3DR know, of the boards that have blown, about 5 have been 3DR, one was mine, caused by severe abuse... and one was Roberts, also a board that took a LOT of abuse.
I agree with you. I meant to post that as a possible explanation of how somebody could read 5v at the 3.3v line even after removal of the regulator. I don't know the board well enough to come up with another explanation of where that 5v could be coming from. Normally I would say that the regulator failed SS, but with the regulator completely removed, the 5v going to the regulator could not pass through. I agree that the dataflash translator is not the problem.
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