With the first radio beacon on-hand, the Sole Survivor is tasked with retrieving a second one, in which the party will stumble upon another rogue robobrain, and its robotic guardians.
After obtaining the first radar beacon and attaching it to Ada, it is revealed that two more will be needed in order to discern the Mechanist's location. Ada reveals that there there is a robobrain at a random location that holds one such radar beacon.
Without needing to attach the second radio beacon immediately, Ada will reveal that the third beacon is located at the Fort Hagen satellite array. She also shares that this means it is in the possession of the local Rust Devils raider gang.
Travel to the Fort Hagen satellite array and bypass the perimeter defenses. Using the terminal on the second story of the eastern satellite, unlock the door guarding the entrance to the Fort Hagen hangar.
Wade through the Rust Devils and their robotic guards to reach the remnants of a dismantled robobrain, designated Jezebel. Jezebel will then cut a deal with the Sole Survivor, in which she will share the secrets of how to gain access to the Mechanist, and in return, she must be taken away from the Rust Devils, and given a new body.
Jezebel will then need to be picked up, and, should the nearby custom sentry bot, designated Ahab, not have been activated beforehand, it will then activate and attack.
Fight through the rest of the hangar and confront the Rust Devil's leader, Ivey. After defeating her, a loot room can be accessed, which will award the unique salvaged assaultron head, and semi-unique assaultron blade, as well as the Mr. Handy buzzsaw. After that, veave the hangar.
Return to a robot workbench, and build a new body for Jezebel, to seal the agreement between the two. She will stick around as a permanent settler (she cannot be used as a companion), and will award the Sole Survivor the schematics needed to access the Mechanist's lair.
Speak to Jezebel again, and receive the schematics
Collect second Radar Beacon
Ada has detected a second Robobrain. I should head out to the location and retrieve its Radar Beacon.
Speak to Ada
I've retrieved a second Radar Beacon from a Robobrain. I should bring the device to Ada, and find out where the third and final Radar Beacon is located.
Proceed to Fort Hagen Satellite Array
Ada has identified the Fort Hagen Satellite Array as the location of the final Robobrain. I should proceed out there to retrieve its Radar Beacon so we can finally locate the Mechanist.
Enter Fort Hagen Hangar
Find the Robobrain
Speak to Jezebel
The signal Ada found seems to be broadcasting from the head of a Robobrain connected to a strange machine. I should attempt to communicate with the head and see if it will relinquish its Radar Beacon.
Exit Fort Hagen Hangar
I've agreed to help the Robobrain head that calls itself "Jezebel" escape from Fort Hagen Hangar. In exchange, Jezebel has agreed to tell me how to access the Mechanist's facility and relinquish its Radar Beacon.
Speak to Ada
I've managed to escape from the Fort Hagen Satellite Array in one piece. I should now give Jezebel's head to Ada so she can remove the final Radar Beacon.
Build Jezebel a Body
In order to discover how to get into the Mechanist's Lair, I should use a robot workbench to build a body for Jezebel's head.
Speak to Jezebel
Now that Jezebel has a body, and I've kept my promise, I should speak to her to find out how to get into the Mechanist's Lair.
Jezebel has informed me that I'll need to outfit a robot with a device called an "M-SAT" in order to gain entry to the Mechanist's Lair. She uploaded the plans for the modification to my Pip-Boy.
For unknown reasons, the quest may fail to register attaching Jezebel's head to an Automatron, preventing the completion of the add-on. On the PC, this can be worked around with the following commands:
Assaultron front actuated frame ·Assaultron head ·Assaultron left arm ·Assaultron legs ·Laser short barrel ·Mr. Handy warmonger spiked plate ·Protectron front actuated frame ·Protectron front warmonger serrated blade ·Robobrain torso ·Robobrain treads ·Sentry Ahab's helm ·Sentry front hydraulic frame ·Sentry right arm