My MG 5570 print double letter for black ink

[Falcon27]

Hi Expert,

My MG 5570 suddenly have problem in printing the double letter. 

It only occur to my black ink.

I tried other color ink (Blue, Red and Yellow) have no problem.

I did some research online and some mention about the encorder strip but I cannot find it in my printer.

Please help.

Reference Pic

http://imgur.com/a/AfLeQ