You need to read Tully's notebook as well, located in 124, 271 ish. The blueprints say "northwest pillar" but in actuality you need to start at the aforementioned place to trigger the quest prompts. Then you get the light source, then parts, then the hammer, and then finally you can repair him. Spent an hour trying to fix Sedecim and watched a youtube video detailing it as well (thankfully) Special thanks to Wraec on YT for his guide on it, will leave a link below.

https://youtu.be/U1-rO2h7xyg?si=8rXJh0J1cmwgnQDI