One motor spinning slower - bad ESC? (motors checked ok)

[grpo]

Hi there,

I'm having a problem with my AIO FC+ESC board from Eachine Novice-II.
One of the motors spins like 30% slower than the other 3 motors.
I'm running bluejay bidirectional firmware on the ESC so I can also see the speed and it shows like 2400 rpm for the problematic motor and 3600 for the other 3 motors. At full power that ratio is 30k rpm versus 39k rpm.
The drone actually flies, because of the very function of the FC, which stabilizes the drone - in this case by slowing down the other 3 motors... so it flies, but lacks power...
I tried to exchange the motors and it appears that the motor connected to the motor 1 pins is always the slowest. I've never seen a half-dead FET, but you never know
It may be a bad FET, or a fet driver, or any other component... I don't know.
I connected the drone today to a betaflight, plugged in the battery (2s), enabled the motors, started the motors with the sliders at 1018 or something (the slowest possible).
Then I clamped my oscilloscope between a ground and the motor's wires.
What I found out is that on a good motor, all three wires show very similar signal to this:



And on the motor 1 two wires show very similar signal to the one above, while the third looks different... the spike is much higher ....



Does anyone understand what's going on there?

 

[Fast and Curious]

Are the coils the same tint as that on one of the functioning motors. Physical damage like the motor sticking or "jamming" in one place, damaged wires or coils and if any magnets have slipped. You have done well and given plenty of information.

 

[grpo]

Hi, @Fast and Curious thank you for your answer. I already wrote "I tried to exchange the motors and it appears that the motor connected to the motor 1 pins is always the slowest." Maybe I wasn't clear enough with this statement. What I wanted to say is that the slowest motor is always the one, connected to the motor 1 pads on the FC. Any motor spins slower when connected to these pads. That's why I'm sure there must be something wrong with the FC/ESC AIO board. Probably FETs or FET driver. I don't know how to inverstigate that since it's all so small and many ICs have their pins on the bottom side. I mean, I can always buy a new FC, but what bothers me is that I've never seen a half-smoked FET and that's what drives me to investigate further.