I'm checking a single tube fluorescent lamp. I measure the stating voltage I get 560v. Trouble shooting book says voltage should be 3 times operating voltage to produce the arc required to light the lamp. Ok 3 x 120 =360v. I measure from one socket to the other. This is instant start. I figure what the heck and flip switch the tube blows. Ballest , bad tube, . Would a bad plunger socket cause this, say it's shorted? What is the best way to check fluorescent lamps.