The tension adjustment knob has a long threaded rod (about 6" long) that has a square metal block that rides back and forth on it as you adjust tension up or down. Over time the lubricant may get dirty, dry, and gummy and clog the threads making the adjustment knob difficult to turn. If you spray an old toothbrush with WD-40 and gently scrub the threads you will clean them. Work the adjustment knob back and forth and the new lubricated threads will allow the metal block to travel freely. The problem will be solved. However....before you can do any of this you have to get the black FRP cover off of the machine. That's not the easiest thing in the world to do, but if you are a little handy you can do it. Email me and I will send you instructions to remove the cover.
cad@gammasports.com