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
Here is my explanation as to the root cause
http://www.rcgroups.com/forums/showpost.php?p=27707120&postcoun...
I proposed that fix a fair while ago http://www.rcgroups.com/forums/showpost.php?p=27214895&postcoun... and I was ridiculed.
Joe, you are completely off track.
The problem with the first board was that Kendall did not cut the trace properly. I fixed it myself. To refresh your memory look at post #115 and #116 on this thread:
http://www.rcgroups.com/forums/showthread.php?t=2007166&page=8
and on post # 123 this thread,Kendall admitted it was his fault, a problem with his xacto knife.:
http://www.rcgroups.com/forums/showthread.php?t=2007166&page=9
Kendall did NOT replace that board.
I emailed him twice about the second board, and he never responded.
I repeat Kendall did NOT replace either ArduFlyer, nor did he offer any support.
Bill Isenberger
Do you have any evidence other than your story about what was found on your board by some unnamed person.
Isn't that your second board ?
Didn't you also damage your first board?
Kendall at UAVOBJECTS assures me that he tested both boards BEFORE he shipped then to you,
Kendall successfully ran the Accel test on both boards before he shipped them to you,
The instant you get the board in your hand [both of them] they magically fail.
You also omitted to mention, that Kendall replaced at not cost to you the first board you damaged, but he refused to replace the second one you damaged, does that have anything to do with these posts, a shorted diode seems not plausible under the circumstances.
Back on page 47, in reply to my original post.
Bill, where are you guys seeing those comments?
I would say that was a sloppy job and not verified - and no customer service as Bill states for that messed up board.
The diode itself - if not defect - wouldn't hurt anything and till someone verifies Joe's theory for him its just a not needed fix at this point.
Don't know, here is what the guy that fixed the board said:
"**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)..."
Bill, so the cure was worse than the disease?
I wonder what caused the diode to fail? Soldering technique?
Turns out it was a bad diode UAV Objects soldered to the board.
According to a third party that repaired the board:
"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."
The problem was fixed by removing the jumper. The sensors aren't damaged and the original 3.3V regulator is also OK.
I agree with PHillip ".. we are all on the same side here....".
And BTW Joe, do you have an explanation for why that one guy on your blog actually had a failed regulator, even with your diode installed?
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