I've got a some hucards that have sticker residue left on them which I can't remove using only my hands. I was wondering if it would be ok to put some water on them as long as I don't touch the contacts? If not, what would be the best way to get rid of this stuff?
It depends on the nature of the "sticky stuff", really.
Water will work -- if the sticky stuff is "sugar" residue left over from organic stuff like candy, yogurt, hot cocoa, candy bars, etc. Water usually *sucks* for adhesive residue left from stickers, tape, labels, etc. Water is ineffectual against sticky grease residue.
Isopropyl Alcohol -- is my *preferred* cleaning agent, not only because it cleans most residue better, but because it dries quickly (try to get as close to 100% alcohol as you can, the less water, the better).
Never use acetone (nail polish remover) or other hardcore products since they can eat a HuCard for breakfast.
Still, some particularly tough residue (certain types of adhesives / grease / crayon) might call for drastic measures. I've used "Goo Gone" for really bad situations. Use Goo Gone at your own risk -- I only use it on the white plastic areas, applied with a cotton swab. Allow the Goo Gone to sit for a little bit and break down the residue. Wipe with a clean cloth when done. The directions recommend a soapy water wipe after this, to remove any Goo Gone residue.
Whatever cleaner you use: Use a cotton swab. In general, I would not only stay away from the contacts, but the ENTIRE "black area", since this is where the PCB ROM is located on 99.99% of HuCards. The rest of the HuCard (that is, the white plastic) is inert.Well, to be precise, there exist a few HuCards whose PCB is longer -- like Street Fighter II -- but you'll notice these because they have a *raised* surface. Also, take note that Ten no ke Bank and Populous HuCards have batteries tucked in there as well.
Note: Alcohol can be used on the "black area" and contacts, just be careful and conservative. Use a cotton swab. I'd never use Goo Gone on the black area though.