Troubleshooting Battery Charger, Impres and Non Impres

[randymince]

I was wondering if anybody had common problems associated with impres and non impres battery chargers. I have a few chargers, all are non impres, that aren't putting out any voltage across the contacts. To open the case, do I need a torx driver with a hollow tip to depress the security dimple on the bottom of the case? I have not troubleshot many of the chargers above replacing the fuse, or cleaning the contacts, but they were standard torx and not the one with the dimple . Any help would be appreciated.