How to clean MVS carts???

I have problems playing a couple of MVS carts.
There is no sound
I have a 1 slot board (MV1-F).

The previous owner is telling me that he had the same problem but after cleaning the connectors it it would work.
So I tried to clean them (cotton with rubbing alcohol) but still no sound...

I was wondering if you had any tips to clean them.
Thanks for your help.

Check out hardmvs.com, great place for stuff like that. They have a pretty indepth walk through on how to clean and maintain your MVS board and games.

If the contacts are REALLY dirty, use a pencil eraser to clean the contacts first, then rubbing alcohol to remove the residue left by the eraser.

Still doesn't work

if several (all?) carts have no sound, I'd look at the board for the prob, not the carts anymore.

I have about 40 carts and only those 2 don't have sound...