Sony WM-GX655 cassette walkman tape speed is not correct

Hi, 

I have a vintage sony walkman wm-gx655, till now it functioned very well, and i mantained it very well too. Recently belt broke and i replaced it with new belt (purchased authentic one from ebay seller). But i feel that tape speed is not correct, need to adjust. can any one help me locate the speed adjust variable resistor for motor on the pcb with a photograph. I do not have a service manual. 

best regards