Had to do some soldering on my Atari recently, so I took the opportunity to take some photos of the mainboard (from both sides since I also had to desolder and replace some components). Not that it’s that much hard to find on the Internet, but here’s my two cents. It’s a 1040STE, however I took the photos with my phone so it’s not the best quality:
Also if you want more info about STE hardware I highly recommend this site.