Revolutionary part of the panel display is not working (4)
I believe the answer is:
Here is my best explanation:
'is not working' is the definition.
(I've seen this before)
'revolutionary part of the panel display' is the wordplay.
'revolutionary' shows that the letters should be reversed in order.
'part of' indicates the answer is hidden within the clue.
'eldi' is hidden in the letters of 'the panel display'.
'eldi' back-to-front is 'IDLE'.
(Other definitions for idle that I've seen before include "Maybe Eric", "Frivolous", "not being engaged", "Futile", "Slothful", "Of engine, tick over", "without basis", "Not in active use", "Not hardworking" and "Explosive stuff".)