It is helpful information you want?

a) Trash the HF charger. Clearly you are not competent to fix it, as they are fundamentally simple beasts with only a few failure modes - Mike pointed that out.
b) Purchase a proper charger from a reasonable source. Amazon has any number of options, just not at $29.99.
c) Read the directions. Carefully. And pay attention to the pretty pictures as only about 35% of Americans can understand written-only directions.

That is helpful information.

Now, try to understand something: The typical car battery contains about as much energy as it takes to operate 6.5 100-watt incandescent lamps for about an hour - at which point, it will be flat,. and probably damaged. However, it can release as much or more than 7.2 KW (that would be kilowatts) for a few seconds - what it does when it starts a car. That is a LOT of energy.. A poorly designed charger puts *you* in danger, as well as the charger. Repeat, a car battery contains a great deal of energy stored in a fast-release system that also happens to use some nasty chemicals. A small portion of that power damaged your old charger - and given your general understanding of the process, it is dubious that any repairs effected by you would be safe for you or those around you.

Peter Wieck
Melrose Park, PA