In layman's terms, how to repair Time Machine back up disk?

I see an exclamation point inside of the my Time Machine logo. I tried a back up and it failed -- many times. I tried repairing it via Disk Utility but that failed as well. Instead, I get this message: I've never encountered a problem with TM. How do I fix it? What's needed?

The disk is toast. Buy another disk.

Damn. Really? Thanks.   

Tom_Reingold said:

The disk is toast. Buy another disk.

Lucky it was your backup disk and not your primary disk. You could recover from that, too, but this will take a lot less time. The point of having backups is that one of your disks is surely going to fail. It's not a question of whether or not it will. It's a question of when. It just happened to you, and because you took a reasonable precaution, you're not screwed. But now you have only one disk, and you better get a new time machine disk quickly, or you're asking for trouble.

For reference if/when my Time Machine disk fails ... Can the disk inside the unit be replaced? Or do you just replace the whole thing?

Apart from the disk the rest is just plastic.

The hard drive is in an enclosure which provides power and cooling. The enclosure outlasts the hard drive. Yes, you can replace the drive in the enclosure if you like to do that sort of thing. It rarely pays, but I've done it and saved a few dollars. But there's a small chance that the failure is the power supply or a shaky power supply caused the hard drive to fail, so I don't recommend it. Plus it's a tricky job.

There is a chance that kthnry is talking about an AirPort Time Capsule which has a hard drive integrated into the router. It is possible to remove and replace hard drives from those with a little Google knowledge and the appropriate screwdriver.

If it's not an AirPort Time Capsule then your Time Machine disk is just a USB hard drive which doesn't have enough other electronics apart from the actual disk to make it worth trying to 'fix'. There's just a dirt-cheap USB interface and the plastic casing.

Agreed and agreed.