Mini 3 Pro cannot turn off and downward vision sensor error after a firmware update [SOLVED]

[xdever]

Hi all,

I have a quite tricky case here, and I definitively can't count on DJI to fix it.

A friend gave me a drone that fell into a lake and was not working. I repaired it (replaced the ESC board, fixed a couple of corroded traces on the mainboard, and resoldered the corroded solder joints of some connectors), and was working fine for a few days, with absolutely no issues, and perfect picture quality (which was quite surprising after being in the water).

Today I felt brave enough to update the firmware which turned out to be a bad idea. After finishing the update, it started not turning off: after counting down the on the LEDs and "turning off" as usual, it immediately starts up again (without the counting action). I can't even charge it because charging works only in the off-state. If I insert the battery, it starts up immediately. Even more strangely, I also got a downward vision sensor error for both bottom cameras. If I try to calibrate it in DJI Assistant 2, the bottom cameras are just black (although the sensor status has a green checkmark, even if I remove the vision board). The distance measurement from the ground, which is also on the bottom sensor board, works.

I would appreciate any feedback. I know, I should throw it away, but I'd still give it a chance if there is any idea what could have happened. I find it very unlikely that two different independent hardware issues came out exactly after a firmware update. I tried refreshing the firmware in Assistant 2, and clearing all data through the app, but nothing changes anything.

Thanks

 

[Cafguy]

Unfortunately your drone has been Swimming, and after that your problem could be almost anywhere. Whether you should give up on getting the drone back in the air really depends on your Electronics skill and wallet but yes I would toss it for sure. you have no idea what will go next. I'm surprised the motors spin.

 

[YVRGUY]

xdever, sounds like a near 100% resuscitation from the lake experience. If you feel confident all the moisture is gone, I would say, that a check up by DJI wouldn’t hurt. DJI will let you decide if you want to continue with any repair. Also, you did not mention the model of drone (Mini 3 I’m assuming) which would most likely weigh heavy on taking repair any further or sending it to the bone yard. In the meantime, you can shelf it for a couple of months while keeping the battery maintained and try spinning the props one more time after that…you never know…moisture does find some very hidden spots that can affect the electronics. Anyways, good attempt at recovery.

 

[Droning on and on...]

You didn't mention the battery... you're using a new one, right? Not the one that was submerged?

I've heard of this problem before, not after being submerged, however the problem turned out to be the battery.

 

[MS Coast]

I very much doubt that the firmware update caused the sensor problem. It's more likely that another problem from the water immersion cropped up.

 

[xdever]

Thanks for the replies.

It was indeed not the firmware, but a corrosion on the compass+vision sensor flex cable connector which I did not notice before. It's a weird coincidence that it was working before but not after the firmware update. It seems like it pulled down the 3.3V to ~2.5V-ish, which seemed to confuse the microcontroller causing the bootups. After cleaning it it works perfectly again, including the downward vision sensors.

a check up by DJI wouldn’t hurt

I'd rather not involve DJI in this, they would get a heart attack if they would see all the hacks and rewiring that I had to do to make it work. The board looked like this when I disassembled it:

Also, you did not mention the model of drone

It is a Mini 3 Pro.

You didn't mention the battery... you're using a new one, right?

I'm still using the submerged one, but I have ordered a new one which is not here yet.

moisture does find some very hidden spots that can affect the electronics

cleaning it in an ultrasound bath with alcohol should dispose the water, in theory. However I did not remove the glued-in flex cables to be able to submerge it in alcohol, and that was exactly the problem now. Also, the already existing corrosion should be cleaned mechanically and the solder joints should be checked. E.g there were some resistors whose pads disappeared (one for the battery smbus pullup and one for the charger battery sense pin).

 

[Droning on and on...]

How long was it submerged? I'm very impressed with how well that battery was sealed...

 

[xdever]

I don't know. I already got it months after it was submerged. The battery got some water as well, I can see the marks on the connector. But the load balancing/protecting circuit in the battery is well protected with some coating: For example, here's a video of Mavic 2:

. Other than that, there is not much that can go wrong: the super big tabs of the battery will take a while to corrode away.