Hacking a GC into a mini - now not booting

[virtvic]

I watched Bringus Studios make a Gamecube mini and I fancied doing this with my spare Cube.
I desoldered all the relevant ports, reattached the SSD2SP and Pico and now it doesn't boot.

Voltages from the power board (soldered to the mainboard) are good.
The led lights up, so does the Pico.
I get a quick flash on screen, then black screen. Fan is functioning ok.

I had another GC, and desoldered all the ports except for the power port. I tested everything and it was just fine.
Removed the power board port, wired the power to the mainboard and now I have exactly the same as the first one

I've checked the fuse on the power board and it is fine. Voltages on the mainboard side are all ok. Is there a fuse on the mainboard?

HELP! - It must be something simple, as it's happened on both. The desoldering all went really nicely - I have a Hakko desolder and it makes light work of those ports.