Cover simple diagnostics and how I replaced broken FET on JHEMCU GHF411
Except perhaps DroneMesh on youtube, very little concrete info for beginners.
Everything is done with POWER OFF. 


There are 2 common ways ESC break. Shorted FET. Dead 5V regulator.

1.
What is a FET? Its a transistor.. a switch.
When there is charge on the gate, electricity flows. Otherwise its open.
Most ESC (30mm, 20mm, and all >15A AIO) have nFET in a square 3x3 or 6x6 mm 8 pin package.

Here is the Toshiba 2R203 on JHEMCU GHF411 AIO





2. 
How do I find what's what?
The Gnd and + pads are easy. You have to find the FET where the short is.
Each motor pad has an identical set of corresponding FET + capacitor + emf magic circuit.

The left pad is connected to the FET on the left, and so on.
I drew 3 arrows. The red arrow is the drain side. The green line is the pin4 gate. The black arrow is the source.
For example: put multimeter in continuity. hold the +, and with other probe, touch any of the 4 left pins. They are connected!


3. 
How do I check my ESC for short?
Set multimeter in continuity (beeping) mode. or measure Ohms.

look at picture above and the red and black arrows.
Hold probe on the motor pad. (Doesn't matter if black/red one).
then
with other probe, touch +, and then gnd. No beeps = OK.

What we are doing is effectively putting probes on the DRAIN, and SOURCE DIRECTLY.
And as you recall from 1st image, unless there is a charge, the switch is open.

*Repeat for all 3 pads, and then for all 4 motors.*


4. 
This is my board. I put X on the broken FET. Motor pad shorted to +. 


5. 
Tricky part. Sometimes you get lucky, and there is space to pull FET up after heating.
But, there is huge risk tweezers will push something.

Solution. Remove all the components marked in green. 2 capacitors, and the Vreg.


6. 
OK. How to do it?
Have the board held by pliers or something steady!
Remove/disconnect everything from the board (I was lazy today)

a) Use small nozzle and low airflow. I set hot air to 460C.

b) I circle over whole board about 8cm / middle finger distance, for 1min to heat board. This prevents thermal shock.

c) Put blob of Amtech NC-559 flux on work area.

d) Get tweezers ready in 2nd hand, and bring hot air about 2 cm straight above the target and make little circles.

e) The solder under the hot air gun turns silver. Be patient! You will see the flux smoking. 
Keep hovering another 10-20sec and gently touch the part. If it moves, pick it up, or push it off the empty area of the board.
DO NOT HIT OR SHAKE THE BOARD.

f) Now re-test the board. Maybe the short disappears after you removed the adjacent capacitor. Or, the broken FET is actually on opposite side of the board. Or you removed the wrong one. This part can be frustrating!!

g) (optional) Tricky part. With almost clean solder iron, tin the pads on the FET while holding it with tweezers.
If done right, the FET will auto-position as it solders and not have cold joint. But too much solder and the important gate can be bridged. Yes, there is already tiny bit of solder left on the board, but the 63/37 we tin flows better.

h) Add big blob of Amtech flux. Position the FET/part as close as possible to target.

i) Like before, start from 8cm away, slowly heating up board, and then "zoom in" on your target.
Be VERY carefull when you are blowing close to the board, because like me, you can blow away other things.

j) As the flux is smoking, keep going another 10-20sec.
ADD MORE flux, and keep going in little circles around the target another 10-20sec.
This makes its not just some of the pads that flowed and soldered.

k) Be patient. Board is very hot. Let it cool slowly.

l) DONT JUST PLUG IN BATTERY! Repeat the continuity checks before.
Don't have a smoke stopper. I have the solution for you! ANY weak battery will do. Even a Duracell 9V. If you dont immediately see bootup LEDs and the ESC chime, it should give you time to pull the plug and save a motor from smoking!

How do you REALLY know if any nFET is working/broken?

1. Set Multimeter to Diode mode
2. Make sure to touch something metal. A Christmas wool sweater can build up static and you will instantly fry anything you touch.
3. Hold and touch ALL the pins of the nFET at same time. This discharges (resets) it.
4. black probe on source, red probe on drain (big pad) -> OPEN CIRCUIT
5. black probe on source, briefly touch red probe to Gate (pin4).
6. black probe on source, red probe on drain (big pad) -> now you see continuity and something like 0.85V.

As you see, all you are doing is moving the red probe.
For the drain, it doesn't matter which pin or the pad underneath - its all 1.
Likewise for the source, it doesn't mattery which of the 3 pins you touch.
 
if you have the little clips on the probe, it makes it much easier.

Great guide for even users like me to learn a thing or two.

Topic should be pinned in the tutorial or motor/esc section.

On 10-15A AIO boards, typically only 12 double-nFET black chips on one side of the board.
On 20A+ AIO boards, typically full set of 24 single-nFET black chips, on BOTH sides of the board.

JHEMCU GHF411 is typically EASY to work on..
EXCEPT this particular FET.

It is pressing against the 5V Vreg to the right, which is touching other things. Its a nightmare.
Took me 4 attempts to get it right!!

This is why Step 5 exists.
Shortcut just leads to endless frustration. When you remove adjacent SMD, its easier to position each.

This is a great detailed write-up. Now pinned in the "Motor, ESC and Prop" sub forum.

Awesome tutorial.
I have so many JHEMCU AIO and Diatone ESCs lying around to try out one day.

I made a thread somewhere listing the FET used by AIO FC.
The ones on iFlight and Mamba are quite popular and easy to get.

For the JHEMCU I bought a bag of 10. I use them on GHF405 and GHF411
https://www.aliexpress.com/item/1005002467585353.html

Excellent Repair Guide.      

 Thanks.

Check out Livyu's channel. Go to videos and scroll down a bit

https://www.youtube.com/c/LivyuFPV

FWIT, looks like JHEMCU on some newer batch of GHF405 25A AIO and GHF411AIO Pro 25A (including mine) began to use Sinopower SM3323NHQA FET instead of Toshiba's.
Got a bag of them myself, just in case ;-)

(01-Feb-2022, 07:01 PM)romangpro Wrote: I made a thread somewhere listing the FET used by AIO FC.
The ones on iFlight and Mamba are quite popular and easy to get.

For the JHEMCU I bought a bag of 10. I use them on GHF405 and GHF411
https://www.aliexpress.com/item/1005002467585353.html

Hi sir. Good day to you and thank you for the AIO FET list... Would you mind sharing the link to your thread sir? As I've looked under your profile for the thread but couldn't find it.
Do you happened to know what type of FET used by DARWINFPV Baby Ape F411 AIO?

the first photo is wrong. - it should be:

My front left motor will beep about 2 seconds after I arm the drone, and will only twitch and not spin smoothly

I am not expert on BLHeli or beep codes.
I recall on github documentation.. what each beep means.

If motor is not spinning, and there is very likely physical damage on ESC.

I have similar problem on GHF411 after de-soldering and replacing BB2 and Fortior.

On one ESC, motor starts trying to spin, then does Beep-Beep and nothing more.