Gaaah. Figured it out. I was following your photos @wermy rather than the text, and some of the test pins (pp8) have moved on the newer Pi zeros, so my SD reader is connected to two GNDs... Mental note: read the words next time.

I'll try shielding tomorrow. Need to check my wiring to the pi as well I think.

@wermy, you weren't kidding about SD cards being temperamental in this thing. I have everything wired up, connectivity all fine, no shorts, but it just won't work. SD card fine in the Pi, not in the cart. I think I might just go without the SD in the cart. Anyone else having any luck?

My 640 screen arrived today. Same control board as Cannikin, and looks to be super easy to wire up. Job for the weekend.

Classic green all the way

You may also get charged import tax when your courier brings it into the UK. Tax on mine was more than the cost of the boards!