Are you doing the Vending Machine Altered Item achievement currently?
are you currently annoyed at how this Altered Item is a complete RNG?

very well, i made this guide cause like you, i am also annoyed by this achievement
also i know this guide was around 1-2 years late from the game release

clarification: this guide was only made as a checklist for all Vending Machine Location in Game. I look up a lot of guide and i never saw anyone provided the location for all Vending machine aside to the Operations Center and to the Abandoned Offices Vending Machines. so before you fast travel or quit and reload the game, i am going to tell you, that there are more vending machines there

in my journey of finding all of these Machines, i found around 14 vending machines scattered around Investigations section and i'm sure i missed some other Vending machine so if you find any location of Machine that i never found, please let me know at the comment section

Overview Map of all Locations


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Vending Machine 1: Sector Head Office, just before the Checkpoint
Nearest Control Point: Sealed Firebreak
note : there are chances Hiss will spawn at this location so yeet them first

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Vending Machine 2: Sector Head Office, before the Firebreak
Nearest Control Point: Sealed Firebreak

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Vending Machine 3: Abandoned Offices, before the security Checkpoint, After the Firebreak if you are facing toward to the Office
Nearest Control Point: Abandoned Offices

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Vending Machine 4: Abandoned Offces, After the Security Checkpoint if you are facing toward to the office
Nearest Control Point: Abandoned Offices
Note: it is near to the Vending Machine 3

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Vending Machine 5: Abandoned Offices, near to the hallway going to the Service tunnel
Nearest Control Point: Abandoned Offices
Note: in my experience, this one has a high chance of becoming Altered Item so if i were you, i'll keep my eye on it

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Vending Machine 6: Operations Center, Upper Floor
Nearest Control Point: Operations Corridor

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Vending Machine 7 and 8: Operations Center, Upper Floor
Nearest Control Point: Operations Corridor, Active Invetsigations
Note: the lcoation of this is in the other side of the Vending Machine 6, between these machines is the control room of the Operations Center, these two, along with the Vending Machine 6, are also a popular location for hunting the Machines

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Vending Machine 9: Active Investigations, Located near the SHUM arcade Machines
Nearest Control Point: Active Investigations

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Vending Machine 10: Fra Mauro AWE wing, located near the Elevator
Nearest Control Point: Fra Mauro AWE Entrance
Note: you can't miss this one because you cannot pass the wing without breaking the door with this at front

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Vending Machine 11: Fra Mauro AWE wing, Observation Deck, Before the Security Check point
Nearest Control Point: Fra Mauro AWE entrance
Note: This is located near both Machine 12 and 10

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Vending Machine 12: Fra Mauro AWE wing, Observatiom Deck, stairs near the Security Checkpoint
Nearest Control Point: Fra Mauro AWE Entrance
Note: this is located near the Machine 11 and 10

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Vending Machine 13: Fra Mauro AWE, AWE Loading Bay
Nearest Control point: AWE Loading bay

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Vending Machine 14: Bright Falls AWE, area after where the Control Point was Located.
Nearest Control Point: Bright Falls AWE Entrance

if you think i miss some Vending Machine in Investigations section please do let me know in the comments because i feel like i miss a Vending Machine despite i already look around.

All of the pictures posted here are my screenshot
the Overview map was also my screenshot but i marked it by my own
the guide cover picture were sketched by me

Thank you for reading and i hope i can ease your suffering trying to achieve this achievement