I have a Black & Decker MT1203 drill, and I have purchased replacement chargers, they charge the battery once, and then never work again.

SOURCE: black and decker cd12c cordless drill Charger

I would guess 12 volts

SOURCE: fixing a cordless drill battery charger

usually transistors have three legs, diodes have two arms all very confusing isn't it? resistors have two arms as well but not three legs or only two legs and no arms its all about arms and legs isn't it do not attempt this repair if you live at home

SOURCE: Circuit diagram for charger for Black & Decker

You can contact a Dewalt Service Center to see if they have the diagram. Black and Decker is Dewalts lower priced line. A quick search on their website did not reveal anything. They may not have the diagram. As far as I know there are no parts available for the chargers so you may have a hard time locating the diagram. Try giving Dewalt a call.

SOURCE: My new Blackmax drill battery charger does not put

You can find a repair center on the link below. You just need to put your zip code in to find the nearest one to you.

http://www.blackmaxtools.com/customer_service/service_center_locator

Good Luck

SOURCE: what is the polarity of a 12v Black & Decker Drill?

centre pin on plug socket is usually positive...
think I would **** it and see ....if the replacement charger has a charge light it will probably not light if you have reversed polarity. Had the same problem with VHF portables ...I just cut the wire on new charger and tried both options ..reconnected and a bit of tape...voila.
There is little danger to your drill from getting it wrong as long as a the timing is relatively short.