Denial

So a couple years back I bought a faulty video cable from 8bitclassics and all this time I thought my Vic20 was dead, only come to find out it was a bad cable all along. I fixed the cable myself (they had wired video out to audio in, grrrrr) and now it works with an old TV that has composite input. But when I try to put this into my RetroTink 2xmini to see it on my hdmi tv, it's only showing a black screen. When I first connect the yellow cable the screen will flicker by in black and white for a split second, but then always goes to full black when fully plugged in. Anyone know what might be going on?