I would definantly look at any switches that might be involved. Some good contact cleaner could be all you need to clean stuff off. Cat urine isn't pretty...I guess you know that by now.
I didn't hear if it was while the unit was on or off. If it was on, something could have been fried by the liquid content of the urine. If it was off at the time, I'd think it would just be your meticulous approach at cleaning. Your black light is good, but it might not shine into areas that liquid can get to, so think like cat urine and where you would go, from the point of contact. Well, I think you know what I mean.
For the smaller access areas, you might have to get some good quality wooden Q-tips. If you have a good quality electronics store near you, you can also get some spatula shaped sponge tipped Q-tip type things, that won't leave cotton frizzies on your components and the spatula shape will also allow you to get down into cracks and even around some corners.
Remember...the cat was just doing what comes naturally to him...marking his territory. But, if you don't limit his access to this room, he will probably come back at some point. If you can't limit his access, maybe a sheet of plastic over your expensive equipment would be in order. You might also put up a sign that says "No Pissing Zone". I don't know if your cat is smart enough to read that, though. Mine are.
Is the cat neutered? If not, he should be. He would be a calmer cat and it would limit a lot of his desire to mark his territory.
