Snes composite issue

I have a first generation SNES (the one with the sound box). When I plug the RCA cables into any TV, the screen turns black and doesn’t show any picture. There are short half second blips of sound, but they happen every 5-10 seconds.

Eventually the TV just says NO SIGNAL. I’ve cleaned out all the pins and the game cartridge multiple times, there is no corrosion. I just replaced the 1.5a fuse, so all my power is good.

I tried the multi out with some cables from my GameCube (which I know work well) yet the same issue happens.

Any ideas to how I could at least get some video to come up?