NRG amp concerns

I have a chance to buy a NRG 201S at a very very cheap price. My question is the guy I am getting it from recieved it from his dad who has passed away and he knows nothing about it. I am going to take a preamp and small speakers to test it. My question is how do I know everything is ok with it. Do I need time to let it warm up and play for awhile or will I know something is wrong right away. Just dont want to throw my money away or back out for that matter. Thanks