Garage door openers just provide automation and convenience. The spring is the real muscle. It provides the majority of the lifting force; it also allows for safe and controlled descent of the door. Torsion springs (what you have) are never at rest, so to speak. When correctly installed, they are always under some tension. As mentioned, a DIYer who gets it wrong during installation or repair will be at risk of significant injury. Please don't try to be penny wise and pound foolish here. Call a pro.