Red Lines on Neo 1 Slot

I just purchased a Neo-Geo 1 slot board and a Samurai Shodown (from different people on eBay), and when I plug them into my SF3 Alpha cab, all of the screens are filled with red lines, and there are red boxes around all of the text. I have 2 other cartridges, but they were sold as-is, and I get only a grid when they are plugged in (no red lines, but the neo-geo splash screen looks normal as well).

My question here is, would this type of issue generally be a cartridge that is bad, or the mainboard? Maybe the monitor needs adjustment? If the cartidge was bad, that would suck, but I got it cheap. If it's the mainboard, I'll need to get upset with someone...

Thanks

Try a cart that you know to work for a fact... it could be a coincidence that all three carts don't work... be sure to clean the contacts of the carts, and the contacts of the mobo (I use one of the old Nintendo NES cartridge cleaners for my two slot)