Find the Minecraft tribute

Find an enemy called Bittersprite on the same map as the Locked Golden Chest. Bittersprite looks like a large wasp or hornet. It is not necessarily near the chest, it can be anywhere on the map. You can see it floating in the top-right area of this screenshot:

Kill the Bittersprite and it will drop a Golden Key. The key will not appear in your inventory when you pick it up, but in the top-right corner of the screen it will say -You Found- and show a picture of the key. You can now open the Locked Golden Chest.

ACT I

Widow's Veil in Crow's Pass

You have to light up all fires and than backtrack to locked door

ACT II

Tower of Moon

It's small arena you have to hit four gongs for secret door to open

Brood Hive

The area for the side quest [Missing Zeraphi] where you have to clear up all eggs. This one does not have any puzzle. You just have to look very carefully

ACT III

Abadoned [cursed] Windmill

You have to read all diaries and find four skeletons attached to wooden beams by axes, when you click on them you will hear ghostly wail and one torch on small graveyard lights up. When all four are "saved" door will open. You have to do this before teleporting to the boss, otherwise you have to enter that area again.

Cacklespit Realm

Destroy all tree stumps, you should open hidden passage. But on my 2nd char its bugged, so maybe you will need to travel back to 2nd city to rebuild new map if that happens to you as well. But when all tree stumps are cut down, you will hear distinct sound. Than go around edges of map on one place logs will appear and create you way for last robot part.

That should be all pieces - now you need to obtain power source from Main quest so its unmissable.