Advanced "motor obstructed" error even with known good motor

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Hello everyone !

I've just bought my first drone last week, a P3A that seems to have been in a crash because the gimbal was completely broken in pieces, but the seller gave me a new spare one that i mounted and its working great. the seller told me that I just had to resolder 2 motors but it was so cheap i think he knew it had a major issue.

so after soldering spare motors he gave me in it seems to be working fine except one motor wont turn on. it just wiggles and gives "motor obstructed" on the DJI GO app even tho i know the motor is ok (i've swapped with a good one and still the same thing on that particular arm).

After a lot of research I'm thinking the ESC might be fried, but i'm not 100% sure because i don't have any esc errors within the app and I tried to test the chips with a multimeter and cannot find a bad one (apparently if there's continuity between certain pins it's dead, but i've got the exact same results than the other good esc's so i'm puzzled)

I've tried everything i can think of, but I've never seen the exact same issue online (everyone seems to have esc errors in the app, but no "motor obstructed").
I've swapped motors, recalibrated the IMU, formatted the SD, and updated to the latest firmware with no change. Maybe i should try downgrading ?

note that sometimes, the drone will accept to takeoff even with the error, resulting in only 3 motors blasting and responding to controls and the 4th not moving at all.


Any advice ? I don't want to buy a new board just yet (it's a V2 and they're expensive). I'd like to figure out which particular part is failing so i can try to fix it myself...
thanks !
 
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When you replaced the motors did you solder the pre-tinned motor fly leads directly to the pads on the mainboard (not cut and spliced)?
 
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thanks for answering! I tried both.

This is a pic a took of the drone when i just bought it. by the look of it and the glue, it seems like the ccw motors were never replaced, but the previous owner had tried to replace the cw ones by soldering the cut wires. he told me that he couldn't do it because the soldering won't stick to the wires but I just had to take the coating off with sandpaper and it soldered fine.

So yes i soldered the spare motors he provided to the cut wires he left in (because he had already cut the motors wires so couldn't solder those directly to the board) and had the issue i described with M2 (front left motor). then i swapped M4 (opposite side wich worked good) with M2 and still got M2 obstructed error. Finally i installed a brand new motor so i could solder it directly to the board, but same thing.

Also i tested with a multimeter the contacts between the battery poles and the wires at the cut and i had equivalent values to M4 so i'm pretty sure the soldering job was fine ? is there any component upstream i should test ?
 

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OK so little update :
i tried testing voltages and this is what i got :

--------------------> while drone "flying"

*from battery poles to motors poles
M1, M3 and M4 : 8v
M2 : 0.5v

*esc mosfets minus to plus
M1, M3 and M4 : 8 volts for each chips for each wire
M2 : 0.5v from first chip, 16v from second chip, same for each wire

---------------------> then i thought that since the drone knows M2 is not working properly (motor obstructed error) it was not powering it correctly anymore so i tried testing while booting up the bird and i briefly got 8 volts for each chip and ditto from battery poles to motor poles, even from M2...
BUT one M2 esc mosfet blew sparks when i tested it !

I'm guessing i found the bad one ?
or maybe there is another mosfet upstream that is blown ?
 
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OK so little update :
i tried testing voltages and this is what i got :

--------------------> while drone "flying"

*from battery poles to motors poles
M1, M3 and M4 : 8v
M2 : 0.5v

*esc mofsets minus to plus
M1, M3 and M4 : 8 volts for each chips for each wire
M2 : 0.5v from first chip, 16v from second chip, same for each wire

---------------------> then i thought that since the drone knows M2 is not working properly (motor obstructed error) it was not powering it correctly anymore so i tried testing while booting up the bird and i briefly got 8 volts for each chip and ditto from battery poles to motor poles, even from M2...
BUT one M2 esc mofset blew sparks when i tested it !

I'm guessing i found the bad one ?
or maybe there is another mofset upstream that is blown ?
It sounds like you created a bad one (killed a mosfet). When you say measuring minus to plus what pins are you talking about?
 
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I hope not, for what it’s worth i tried rebooting after and it just behaved exatly as before... I couldn’t find a way to figure out wich one is the bad one (if any) because they all gave the same values and this particular mosfet is the only one in the entire board that did this. Note that when testing this one again touching another top pin it didn’t spark.

I did some researsch and it seems that when looking at the mosfet with the circle in the bottom left corner, the gate is the pin in the bottom right so i measured between any top ones and bottom left.
 
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If the motor turns freely my money is on poorly executed electrical termination if the motor wires.
Would you say that esc are fine because if they weren’t i’d be getting an esc related error and not only « motor obstructed » in the dji go app ?

What do you mean by poorly executed electrical termination ? Are you implying bad soldering job ? Sorry English is not my main language and i want to make sure i’m understanding correctly.

If so then I hope you’re right, but I’ve tried 3 different good motors at that particular spot, resoldering each time either from cut wires or from motherboard pads, and i’ve tested good values from battery poles to cut wire between board pads and motors so that means soldering is fine doesn’t it ?
Plus i’ve swapped 3 times the opposite motor and it works just fine so i’m puzzled about that. Any way to test it ?
 
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Would you say that esc are fine because if they weren’t i’d be getting an esc related error and not only « motor obstructed » in the dji go app ?

What do you mean by poorly executed electrical termination ? Are you implying bad soldering job ? Sorry English is not my main language and i want to make sure i’m understanding correctly.

If so then I hope you’re right, but I’ve tried 3 different good motors at that particular spot, resoldering each time either from cut wires or from motherboard pads, and i’ve tested good values from battery poles to cut wire between board pads and motors so that means soldering is fine doesn’t it ?
Plus i’ve swapped 3 times the opposite motor and it works just fine so i’m puzzled about that. Any way to test it ?
Yes I was suspecting poor soldering job, assuming the prior owners handy work as you clearly know the issue with the insulation on the motor wires.

And yes I had also expected to see an ESC error.

From what you have said with the motor working in other positions it does unfortunately seem like the ESC is dead.
 
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Okay thanks for your help !

I wish i knew for sure which chip failed so i can try and replace it...
not having any esc errors seems really strange and i wonder if something else could cause this.

I don’t think this is an usual case of fried esc and suspect something wrong upstream. Current seems to be flowing fine when booting, so mosfets ARE capable of doing a good job and the gate isn’t open at all times if i can get 8v on each chip on startup...
there must be something wrong occuring after this !
 
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Just want to give yet another "thumbs up" to the staff at 'Go Unmanned' in Raleigh NC. They do amazing repair work, I've had my P3P as well as my P4P worked on there. Recently my new(private purchaser so no warranty) P4 OBSIDIAN just flew great one day, next day no image transmission as well as 'gimbal disconnected' at the bottom of that screen. I tried every self help diagnosis on line for weeks. Finally sent it to them last monday. He found the same issue and the histogram won't even let you turn it on so it was bad. I located a refurbished by dji from dji .P4 Obsidian camera and shipped it wednesday. I received my package yesterday and it works like a dream. I had to buy the camera of course(less than$450.00) but my invoice from Go Unmanned was $120.00 including $50 UPS overnite. I'm in Northeastern Nc about 100 miles from them but they have been perfect to work with, and they work on ALL things dji So, if you need it fixed right, these guys are at Go Unmanned 533 Pylon Dr.Raleigh NC 27606 919-835-2140 when you get the drones prompt press 2 and Sierra is in the office. Ask for Max to check out your problem. I told him I was sending them business for 6 months. Just mention I referred you to them, its not a $ thing....IT's a CAROLINA THING.....Peace
 
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After careful inspection of the board and testing of the mosfets, i cannot pinpoint the issue.

I’ve ordered a working replacement motherboard for a good price so i’m just going to swap it and hopefully i’ll be flying happy soon :)

I would have changed the mosfets if i could identify a bad one or had an esc error but i’m pretty sure it’s a more complicated problem.

Anyway thanks again for your guidance !
 

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