Trying to fix my SNES black screen

Hi all, I have a SNES that frequently shows a black screen, only working sometimes. I've cleaned the cartridge slot with isopropyl alcohol, but no luck. The power led turns on, so it's not the fuse. I've checked out the motherboard, but it looks okay. See these pictures:

http://imgur.com/a/JvlBK

Is it possible that it might be a problem with the capacitors? I'm not an electrical engineer, so I don't know how to recognize bad caps. I am however capable of soldering.
Or is there a different solution to the black screen?

 

It works sometimes?
When it is working try tapping on the cart while it runs.
Can still be a bad contact in the cartidge slot. Or maybe a cold solder joint.

 

Moved to the correct forum - the Nintendo development forum is more for discussing development on Nintendo platforms ;-)

The first step to fault finding is testing power - check the PSU, check the chips are getting the right voltages etc. Make sure you're using a known good game, too. And yes, check the continuity from cart to motherboard.