I have blown up two modules. Both Dyna, one, a Dyna III and two, a Booster. I think they actually may be the same unit. They look the same but I don't have them side by side to compare.
The Dyna III was blown up by my stupidity, I was balancing the carbs by lifting the plug wires. This unit did not stop working all at once but seemed to get weaker and weaker over a period of almost a week and finally the bike wouldn't start.
The Booster gave out with no warning. It was exposed to cooling air flow. I had not been balancing the carbs by lifting the plug wires. It just went.
These units can be bought over the counter in many places or ordered on line from many sources. You can even buy them from the manufacturer. The one that works on our Airheads is the DBR-1. It is hard to find this thing on the DynaTek site because they want us to buy more expensive products. But the Booster is on this page;
I have no connection with Dyna. I would almost prefer to find something else but then I also have nothing against Dyna.
You don't have to run out and get one of these right away. It is a nice modification to do when you have the time. You may find other units attractive. There are many long threads on AdvRider about these, I'm in a few of them, you may want to build your own. I think the Dyna unit recently went up again, it's now $87. You can build something that is almost the same thing for less than $25. Sorry I don't have the directions. I'm all for that approach but I've never done it.