I got a small 2600 today, possibly the Junior, although it doesn't say that anywhere on it, or the box. (I expect you can tell I don't know anything about Atari consoles)

It works fine except for the action button. I've tried different controllers, and I've tried those controllers on other consoles. But the action button doesn't work with any of them on the 2600, despite being working controllers.

I've cleaned the pins on the controller port and I've checked the solder points. All I can think of is maybe a chip is fried. What can I do about it, besides spending months looking for another one?