My son has PS2 7000 series. It never functions with a second controller.
At first, we thought that the problem is with the controller so we changed it. But it still didn't work.
Then we bought multitap, considering that the problem may be with the slot. But still, the issue persists.
For example, if he plays Dragon Ball Z, the option for 1p VS 2p is disabled. In any multiplayer game, the option for the second player is inactive. By any game, I really mean ANY Game.
We tried more than 10 different games but no luck.
What could be the problem?