Which word to use, in part, depends on whether you want to indicate only that the devices and machinery have not been properly maintained or also the resulting impaired function.
Neglected and untended, would describe something not taken care of, as would quite a few synonyms, such as abandonded, overlooked, or forgotten, and one might assume items so described would not be working well.
Dilapidated and decrepit, as well as ramshackle and rickety, are similar, and would give a stronger suggestion that the item is falling apart or broken down and likely not working well or at all as a result of neglect.
You could use dysfunctional, as well as debilitated, crippled, impaired, or unusable, but these don't really indicate that the condition is the result of neglect.