After automatically becoming an employee of Jakobs Corporation in Dead Haven, you are given the chance to buy equipment from a Jakobs-branded Vending Machine. According to the PA system on Jakobs Cove, as an employee it is an obligation to use Jakobs branded equipment ("If it ain't a Jakobs, I'd rather be dead")
Find a power coupling and repair the Jakobs vending machine.
Power coupling: 0/1
Coupling installed: 0/1
"To anyone attempting to survive in Jakobs Cove: This is a Jakobs company vending machine in town that could help you deal with Dr. Ned. It may need a new power coupling, but if you're able to repair the machine, you can gain access to its inventory - something which could help you survive. Remember, if it just needs to be dead, it needs to be Jakobs. These zombies need to be dead."
Once you insert the coupling, the machine is active and ready to be used.
When you turn off the game system the machine is no longer active. And may not be reactivated. Timer does reset as a normal machine as long as you do not turn your game system off.
It also becomes unusable when leaving the main map (Jakobs cove main town, even though staying in the DLC areas) for a (long) period of time. It is usable again after completing (certain) missions at the bounty board. (Without quitting the game.)
Power Coupling: "A stolen power coupling for the Jakobs vendor." As it is found next to the corpse of a bandit, it would seem that the said bandit was its thief but was killed before he could get away.
Even though it is supposed to be a Jakobs vending machine, it often will not have a single Jakobs weapon available.