I'm having issues with the unit reading games. (Details inside)

I recently bought a non-working unit from ebay for cheap. I saw that the battery terminals were corroded and that they were in desperate need of a cleaning. I also noted that there was a small, albeit significant, amount of corrosion on the board. Foolishly, I chose to disregard it, as the issue with the terminals was solved and the unit was able to power on and display the startup logo. It seemed like it was in 'working condition' at that point, but it refused to register/ play games when I tested it later. The furthest I got was the Nintendo logo with Tetris, and when I tested Pokemon Blue, the unit went berserk! There were wavy lines all over the screen! The unit also made a buzzing sound, which totally freaked me out. Whether or not the non-working speakers emitted it I am not certain, but it was enough to completely scare me away from ever giving power to the board again. Cleaning the cartridge didn't yield any results, so I investigated further. I disassembled the unit once more and found that the corrosion had traveled inside of the game port. Crap! So much for my cheap project! Does anyone have any advice on how to fix this? I'd also appreciate if anyone could provide an explanation on the mysterious lines and buzzing noise, as they were very unnerving. I'll provide pictures if need be.