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
I bought regulators for APM2.5.2 : TPS79133DBVR with the intention of replacing them but I wasn't careful enough when removing the damaged regulator and managed to pull the "ground" and "in" solder tabs off the board and I suspect its now damaged beyond repair.
I've now moved on to the Pixhawk instead of replacing the APM.
I have two remaining regulators (296-11866-1-ND) in Australia and am happy to post them to anyone in Australia (local post only). Please PM me and I'll post them to you in a padded bag with pleasure.
I had one go out on a new RC Timer ArduFlyer. jabram suggest it might relate to a USB with low voltage, on the front of my computer, or a bad lipo that dropped voltage while I was setting up. Discussion and photos on this RCGroups thread:
http://www.rcgroups.com/forums/showthread.php?t=2007166&page=10
Bill, that is an interesting thread.
Has Joe suggested what the actual mechanism is, whereby a low 5Vcc from your USB could cause the 3.3V regulator to fail? I can't figure that out at all. Since the 3.3V reg is a super low dropout, it should have no problem at all down to a 5Vcc of about 3.4V. Your USB was putting out more than that. And even should it go below that, an LDO usually fails "well", it simply puts out less voltage. At 3.0V input, it would put out 2.9V.
Joe tends to guess at things, and provides no backup information or data, so you have to take what he says with a grain of salt.
I see that your board already has the "protection diode" installed, which is something else that he came up with. Previously he has stated that this is the cause of the failures. But now you've had a failure, despite that diode being installed. So now we're guessing again.
I'd like to suggest another cause, that is at least plausible.
You are using a UBEC to power the board of unknown construction or quality. Have you or anybody else ever checked the output of it on an oscilloscope to see if it is spiking over 6V on power up? Using this external BEC instead of the dedicated voltage input on the APM board, bypasses the the overvoltage protection circuitry, leaving you vulnerable to this sort of thing.
Another idea, and this is admittedly grasping at straws a bit, but something to think about... Some switching regulators (UBEC's) will fail very badly when they go undervoltage (you had that bad battery). Some of them will actually pass through full unregulated voltage when that happens. Not a good thing. Again, you've bypassed the protection circuitry.
Hi Robert
I think that your UBEC theory fits perfectly with what i experienced yesterday.
I had a perfectly good arduflyer board that i was using to test my (testbench components) to make sure they where all adequate. (usb cable, power source, etc)
No bad gyro, good compass calibration, good gps lock (even in my basement), etc..
Recycled the board a few times and reconnected (without changing any connections)
At some point i disconnected the power from my 12v power supply to the bec and reconnected it...
I reconnected via 3d radio.... as i did before...., good connection, BUT oups...... bad gyro health....and the horizon started going awire....
I instantly checked the 3.3v regulator...... and got a 5v..
I decided to check the ubec output peak at power on..... and yep, i get a 5.9 peak for a split second...
I wish i would have seen your post before......
The ubec used is a Hobbyking low noise Ubec... http://www.hobbyking.com/hobbyking/store/__4319__TURNIGY_3A_UBEC_w_...
The one that Jabramm is showing on arduflyer build thread..
Hope this info will help in the troubleshooting, but for me, the only thing that i did was recycling the power.
So that's it for me..... now i need replace those regulators....
....
Mario,
That's great feedback. So we now know that it doesn't require you to do anything silly like plug an ESC cable in backwards to cause the failure.
Tried 2 identical HK becs
i get a steady 5.98 on the first when connecting and then it goes down to 5.23
The second one gives me 5.88 and goes to 5.22.
Not shure if that 5.98 peek is long enough to blow the Vreg, but if it is, no wonder i now have 3 blown boards.... Especially since this Ubec is a permanent component of my testbench.
HI,
Unfortunatly, i dont have a scope and my voltmeters are not top quality either. Nevertheless, i tried with two different multimeters and they both give me about the same high peaks.
I tried another HK bec ( a bigger one)
http://www.hobbyking.com/hobbyking/store/__6320__TURNIGY_5_7_5A_8_4...
i get 5.5 peak on this one.
All my measures (even the previous) where taken with the ubecs set on 5volts.
Hi
the bec was measured with a voltmeter with no load on it. Mind you, i have a similar one on an hexa with an arduflyer and i had no problems with it yet.
http://www.hobbyking.com/hobbyking/store/__6233__TURNIGY_8_15A_UBEC...
I will check it later on today
Sorry, i realized that the post was by MOCHABOY and NOT JABRAAM on rcgroup http://www.rcgroups.com/forums/showpost.php?p=24263408&postcount=1
I ended up sending my Arduflyer off to have the 3.3v regulator repaired and this is what was determined:
"the diode on jabram's diode fix was dead/shorted on your board, and that *whoever* performed the mod used a bad part and didn't bother to test it afterwards. Either that, or there might be a possible issue with the fix itself that causes the diode to blow out (doubt it, but I guess you never know)..."
The problem was fixed by removing the jumper. The sensors aren't damaged and the original 3.3V regulator is also OK.
According to the thrid party that did the repair:
"The actual diode itself appears to be fried/damaged, so it was basically creating a short-circuit from the 5V rail to the 3.3V rail. It's as if you would have bypassed the 3.3V regulator altogether and sent 5V to the sensors."
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