The wiring is very basic, but i dont have a camera today. I can explain the wiring:
the arduino is connected to the computer via usb, the 5V from arduino goes to the logic on the motor controller. All 4 motors are connected to their power source on the motor controller (the motor controller is connected to 6 AA 1.5V batteries). 4 PWM from the arduino are connected to the PWM of every motor. All grounds are connected to one main ground. nothing more nothing less.
All 4 motors were connected identically, only one stopped working while the others are still fine.
it looks like the same problem that happened to me. Unfortunately I don’t know the cause for it. Only a vague suspicion: Maybe a loose logic power supply connector was the cause. I have used Jumper cables with round pins, that didn’t give good contact. Now I use the srew terminals. No more problems so far.
Because I need only 2 out of 4 motor drivers I have no urgent intention to replace the defect one. Don’t found the SP8M3 at my favorite distributors list, too. A replacement part could be the IRF7319. But in this case you should replace both half bridge ICs U7 and U8.
Replacement of the chip is not a big deal if you know how:
Use a cutter to cut off the pins of the defect IC.
Than remove the pins with the solder iron.
Than you can solder the new chip.
Hold it down with a pincette and solder one pin first.
If everything is in the right place continue with the other pins
Edit: I have some IRF7319 chips here, so I will try it by myself.