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 subsidiary indication.
'revolutionary' shows that the letters should be reversed in order.
'part of' indicates a hidden word.
'eldi' is hidden in the letters of 'the panel display'.
'eldi' written backwards gives 'idle'.
(Other definitions for idle that I've seen before include "Good-for-nothing", "Ineffectual", "Out of work", "Lazy - vain", "Of engine, tick over", "Reluctant to work - Pythonesque Eric", "Inactive - lied (anag)", "Not busy", "Without work" and "lndolent".)