Google posted on the AdSense Google+ channel that the ad balancer tool which is a tool that can be used to show less lower paying ads on your site, is not back up and running.

Google wrote:

I had no idea it broke – to be honest.

Here is what it looks like:

Here is a screen shot of the tool:

You can drag and click apply to adjust your ad balance:

Forum discussion at Google+.

Update: Now when I try it, it says it is under maintenance…