TOMIX DCC conversion Motor rectifier?

[DennisAkaTECHNO]

Hey folks,

I've just started taking my TOMIX HO series 683 apart and found this little circuit board attatched to the side of the motor:
 

 

I've converted a Kato EF65 and a TOMIX EF210 before and both of them haven't had such circuits near the motor.

My observations so far: Motor starts spinning a lot earlier and faster without the circuit board (at 0.7V) than with the circuit board (~2.5V).

 

As far as I can tell, there's a rectifier and a rectifier diode on the board, but not sure what the green SMD part on the left is.

 

Do I need to remove this to run DCC, or can I simply leave it how it is? Wouldn't I lose the slow speed ability if I remove it?

 

Greets

Dennis