A twig managed to shear off a mosfet from the 4-in-1 ESC board of my JJRC X1. This caused an avalanche of fried mosfets. At least three others blew up as well. I decided to replace all of the mosfets from one of the ESC channels, just to be sure.

(This is the board with the missing mosfet. Note that my X1 frame broke at some point and I have built the electronics into a cheap Q250 frame since)

Spare parts

Originally the board uses the AO4720 (n-channel), AO4407A (p-channel) and the 2sk3018 n-channel driver. My local dealer did not have both of the power mosfets so I found some compatible types otherwise I would have had to wait for the slow boat to arrive from China:

• AO4720 -> IRF4713ZTR
• AO4407A -> FDS6679AZ

I selected the replacement types mostly to match the max Vds (same or higher), Rds (on resistance, lower is better), Vgs (should be the same ideally) and maximum switching current (Ids, same or higher current).

Rework

Remove the old mosfets with a rework station. Clean up the leftover solder with some desolder braid.

Solder the new components and make sure to have the orientation correct otherwise you will make more smoke.

On the backside we replace 6 fets, three SO8 packages and for good measure we also replace the three driver fets. In the photo below I have removed all 6 of them.

After soldering the new mosfets the ESC seems to work as before. Luckily only the mosfets were damaged and not one of the outputs of the microcontroller on the ESC. That would have been a more serious issue...