It sounds like more than a brake issue if you're right. I'd call tennis machines back assuming that is where you got it. Is this a new or reconditioned machine? All you should need to send them is the crank tensioner assembly and not the whole machine.
Everyone has the right to be stupid... it's just that some people abuse the privilege...
Balance - 31.0 cm, Weight - 358 g, SW - 346 Kgcm^2