Reader be warned, this is a technical writeup, and I will be using advanced terms such as "thingy" and "sound". Proceed with caution.
The elf is about to die!
The Atari audio regulator board is a very common component in almost all arcade games produced by Atari. Without it you don't get to hear the booms in Asteroids, the digitized speech in Gauntlet, or the hippity hopping in Kangaroo.
There were many versions of the audio regulator board. But the most common one was the AR II board, which is what is used in most classic Atari titles. The AR II board is basically a smart amplifier. It doesn't just amplify the sound, it also checks to make sure that the game PCB is putting out enough sound in the first place, if not then it cranks up the volume to compensate. It runs off of +5 Volt power from your game's power supply, and connects with several plastic connectors.
What to do when Dig Dug goes silent on you.
It is always a sad thing when you drop that quarter in, and are greeted with total silence from your favorite game. Audio regulator boards are a common point of failure with many games. This is mostly due to the fact that Atari overengineered the darn things. A very common failure is the capacitor at location R-29. The exact location varies from AR board to AR board, but it is labeled. This one tends to fail if your game doesn't have a good connection between the AR board and the main PCB, so what the game ends up doing is wildly overcompensating, and shunting power directly through the R-29 spot. If your AR board is heating up, then you may have a bad connection. Remove the connectors and examine them, you may have to use a paper clip to pull the little metal connector thingies out a bit, so they make a better connection. Checking this can save you from having to repair your AR board in the future.
You have a few options if your AR II board has already gone dead. You can technically replace it with any small amplifier that will run off the available power in your cabinet, this will require a little custom wiring though, and it will slightly devalue your game. The better solution is to get an AR repair kit, and fix your own board. It is a straightforward thing, and anyone who can use a soldering iron can do it. Repair kits are usually under $15, and replacement AR boards are usually around $30 or so (prices current as of September 2002). It is easy and cheap to fix the missing sound that many Atari games are afflicted with, so there is no excuse for a silent Tempest machine.
You can buy affordable AR repair kits from Bob Roberts at www.therealboboroberts.com.