Using electronics is old hat on board — rubbish diode, ultimately (5-5)
I believe the answer is:
solid-state
'using electronics' is the definition.
(as in solid-state electronics)
'old hat on board rubbish diode ultimately' is the wordplay.
'old' becomes 'sos' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hat' becomes 'lid' (synonyms).
'on board' is an insertion indicator.
'rubbish' becomes 'tat' (I've seen this before).
'ultimately' suggests the final letters.
The final letter of 'diode' is 'e'.
'sos' placed around 'lid' is 'solids'.
'solids'+'tat'+'e'='SOLID-STATE'
'is' acts as a link.
(Other definitions for solid-state that I've seen before include "Using semiconductors" , "using only chips?" .)