Introduction: FIX a FRIED ESC!

About: I am new to instructables and have a lot of interest in diy projects and want to build more multirotors in the near future. For the time being I have designed quite a many of them! I also love etching circui...

Having Crashes are fun! But having an ESC to blow up during flight is not fun at all especially if its on a multirotor!

What are FETs?

FET is a short form of mosfetFet. FETs in an esc is just an electronic switch which switches voltages between the three wires which causes the motor to turn. what often happens is that the FETs have a lot of switching due to high current draw and that causes them to over heat and fail.

Or sometimes the heatsink are not properly in contact with them, which causes them to over heat and fail!

Here's a few steps on fixing your fried ESC:


• An Old Motherboard
• A Soldering Iron
• Piece Of Heatshrink (could use tape)
• A Heat Gun (optional (If you are good at desoldering with a solderig iron then there is no need to buy one or if you have it use it )


Steps to remove the FET from the Motherboard!

• Use a Heat Gun (the gun which blows out hot air)
• After a couple of minutes take a screwdriver and slide the FET out of place.

You could also use a soldering iron if you are skilled. (trust me don't do that. But if you can do it, do it) This way may damage the FET.

OR The other way!- this way is dangerous but faster!

• Find the FETs closest to the border of the PCB.
• Turn on your cooking stove to high flame!
• heat the under side of the FETs (Don't heat for too long (less than 25 seconds) and DON'T INHALE THE SMOKE Given out)
• Take a screwdriver and slide out the FETs. (lol I used a lighter at that time :P)

Step 3: Removing the Failed FETs From the ESC

• Take apart the ESC's heat shrink
• Remove the heatsink (the aluminium thingy)
• find the faulty FET (Usually the FET will be half broken or it may be bulging out)
• use a heat gun or desolder it (heat gun would be better)
• if using the heat gun heat the FET for 30 -40 seconds
• try to move the FET with a screwdriver while heating it.
• finally it should come out!

The next step has the video of me removing and replacing the fet with a soldering iron!. so watch that video :)

Step 4: Placing the FETs On!

Follow the video!

Just tape it up or put some heatshrink! and you are ready to go!

Oh and don't forget to replace the heatsink!

(After soldering please check for shorts in the circuit)

Step 5: DONE!





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20 Discussions

Technically FET is a family of transistors and MOSFET is a subgroup of that family. JFETs were the first type of FET. Although most FETs that you run into today will be MOSFETs. Especially the large power handling type like you are working with here.

5 replies

It may be important to add that there are 2 major types of MOSFETs: P channel, and N channel. It is most common to see N channel, but P channel is not unheard of. Where N channel MOSFETs are used for low side switching, P channel is opposite and is better suited for high side switching. It may be important to research the part numbers, and see which type need replacing, and which type is salvaged.


I actually repaired my hubsan X4 this way. One day I decided to pull it apart to see what is inside, and I noticed the microphone area was unpopulated. The sound quality from it's recordings was really quiet, and the fact that it was probably just picking up pure electrical noise would explain that! I went ahead and installed the smallest mic I had, and after tring to find a place to fit it, and trial and error, I finally gave up on it. When I went to use it, however, I did not notice that I had made a tiny solder bridge form across one of the motors. Unknowingly, when I put it all back together and tried to fly, I killed the motor output, I noticed at first when I armed it and revved up the throttle, that it would black-out and not fly, as if it was a completly dead or really weak battery. Then I smelled really faint, almost unnoticeable magic smoke and the thing game back to life and flipped out! I noticed that motor no longer worked!

After pulling it apart again, I noticed what had happened, and the TINY fets, the ones in pain-on-the-butt SOT-23, that one of them was ever so slightly charred. It was barely visible, and it took awhile for me to confirm that under a telescope eyepiece lens. (that smell is simply unmistakable, no matter how faint!) I found that after some research, that they were indeed 3A FETs and not BJT transistors, so I pulled out the old LED driver from a cree XM-L flashlight circuit that had been replaced for other reasons, which had to have similar ratings; given that the XML LED driver had been rated for 3.3V @ 3A, and had 2 similar looking SOT23 packages on it. I stuck the iron on it and got it off, and soldered some really thin magnet wires to the 3 pins, and connected it to a really simple LED circuit to test and confirm it was indeed an N channel FET. I then replaced the charred one on the hubsan X4 flight controller with that new shiny one. And got a chance to do some SMB work on tiny stuff for the first time: You sure learn skills quick when franticly trying to fix crap LOL!

Now it almost works flawlessly! Well almost, that one blade would now always twitch when powered on. Turns out I accidentally removed a small resistor close to the base, and there was no way I was going to get that resistor back on where is belongs, it was just far too small: practically microscopic, easily mistaken once off the board, glued to the iron, as a for a bit of dirt! Nor did it even have any value or number printed on it! So for uniformity, I did that same thing to all 4 resistors next to their respective motor driver FETs. Now all the blades twitch on power up, so it seems normal. My guess is that it occurs when the microprocessor inside is booting up, and tests all the outputs to make sure they initialized and work, not sure though! Trying to draw a carbon track across the pads with a pencil did not help much)

Hahaha that indeed is an amazing story! ??? Enjoyed reading it! :D

I did eventually end up replacing the whole control board on that micro quad, as I later fried the 3V LDO regulator on it too! (I tried to fix this by using an LED as a shunt regulator, but that failed)

Also, to make it so all the motors twitch and to verify the missing resistor on the replaced FET was the cause, I removed all of those resistors. Turns out the purpose of those resistors was to prevent spurious voltages building up on the MOSFET gates before the microcontroller enables those pins as outputs.

Worse yet with the old damaged control board, if I crashed hard, the micro would enter a "panic" state (all LEDs synchronously flashing, telling me an error) and the motors would rev to FULL SPEED! I think this is because when it enters this panic state, the micro disables the output pins, and rely's on the pulldown resistors to keep the MOSFETs off. Oops.

You at least got to learn something from that quadcopter and sure did I! :D It's seems pretty amazing that a tiny resistor can potentially have such a great impact on how the system operates. Truly amazing!

A couple of years back, I remember trying to add another channel on one of the chinese radios. I went through the whole circuit board to find out which pin does what and what pin goes where, all because of an empty test pin with CH7 written on the side of it that intrigued me. After a lot of trials and errors, it didn't seem to work... Looked like they probably had that pin purposely locked from the factory. In that process I learned SO much! Reverse engineering is really fun once you get into it!

how can i find out which one is failed?

The video stil does not work

1 reply

Hey the video doesn't explain anything it just shows how to solder new MosFets on to the esc.

Connect the 'Source' of the MosFet to the meter's negative (-) lead.

1) Hold the MosFet by the case or the tab but don't touch the metal parts of the test probes with any of the other MosFet's terminals until needed.

2) First, touch the meter positive lead onto the MosFet's 'Gate'.

3) Now move the positive probe to the 'Drain'. You should get a 'low' reading. The MosFet's internal capacitance on the gate has now been charged up by the meter and the device is 'turned-on'.

4) With the meter positive still connected to the drain, touch a finger between source and gate (and drain if you like, it does not matter at this stage). The gate will be discharged through your finger and the meter reading should go high, indicating a non-conductive device.

Such a simple test is not 100% -- but is useful and usually adequate.

Hi is there a way to know what's wrong with an esc? Mine just moving servos but no motor. Cannot see defect in switches.

Will post the video again thanks for telling me! :D

You should also look up the part numbers to make sure that you got a simliar mosfet (there are many types, don't mix n and p-channel, check the pinout as well) , not just a component in the same package. Since you most likely need to look in the datasheets anyway, it won't hurt to compare the maximum current rating (higher is better) and the gate capacitance (lower is better).

Besides that, great instructable. People need to get aware of the benifits repairing offers: it's cheaper, in most cases rather simple and reduces waste :)

keep repairing :)

PS: Did you also have desoldered that huge BGA in the top left corner? It looks like that :)

1 reply

Thank you for such an awesome comment! I will surely create an update which includes the details about the data sheet. And yes I did remove the intel BGA chip from there for fun! :D

if you are going to use fire, better off just buying a replacement.

1 reply

I did this method just because it is faster to do. Rather than waiting for a month for my parcel to come from china