Unblock the eco beam was a mission that Jak and Daxter completed to obtain a power cell in The Precursor Legacy. The eco beam that provided power to Sandover Village was blocked by Lurkers, until the Mayor asked Jak to go and unblock the beam who did so. After that, the mission was renamed to Connect the eco beams, which he also did, after which Daxter prompted him to return to the Mayor for the power cell, temporarily renaming the mission Return to the Mayor.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Shiny Happy Steeples", completing this mission will reward you with a silver trophy.
After passing over the first bridge, follow the path leading forwards, crossing the river to the left by either using the tree stumps or by walking across. From here walk around the temple to the right. You will notice a large Lurker-made machine, use the three moving pistons to jump on top of the machine. Jump across the rotating discs on the top, and break the mirror redirecting the blue eco beam, which also powers down the machinery.
After this a wooden pole with a mirror on-top will rise from the ground behind the construction. Using the handles at the base you have to to redirect the beam. This is done via a small screen where you just have to point the cursor at the next mirror which will rise and show itself automatically. After this, walk over to the area where you had to redirect the beam, find the next beam redirector, and repeat the process.
Eventually you will have to redirect it into the Mayor's windmill, where after you can pick up the power cell at his house.