How to setup on turntable

I have problem on Thoren 318 MKII turntable. Somehow the sound of one channel has less sound and more humb. I opened turntable and try to see inside. I wonder that if I want to setup or install the arm, catridge or niddles. How can I start from ground up? I do not have manual to setup or any idea to do it. Can you explain how to setup? Maybe learn to setup. I use Sunfire amp and processor to setup. Any way to buy or look for manual 318 MKII.