Icom A6 car adapter CP20

Recently I acquired an Icom A6 in the "Sports pack" version, i.e.
including an adapter for the car lighter plug. This adapter is called a
CP20. Through a slight mistake in my car cabling, I managed to connect
it to the battery the wrong way around, plus and minus were inversed.
Yes yes it's stupid don't tell me. The lighter plug contains a fuse (8
Amp!) I replaced that but still the radio won't work, I suppose
something in the CP20 blew quicker than the fuse.
NB the radio itself is fine, works like a charm on 6xAA batteries.

Two questions now:
-) how to open the CP20? There seem to be four small covers over screw
heads, but they won't move for any effort I applied. Drill through them?
-) any suggestions as to the CP-20's insides? Schematics, perhaps? What
are the most obvious candidate victims?

TIA,
KA