hi,
First use warm water with added detergent, say pot washing liquid, then rinse thoroughly with deionised water.
Allow to dry, a woman's hair drier used carefully will increase the drying speed.
Inspect for for any copper track or wires which are 'green' with verdigris, clean and reconnect any broken tracks.
Plug in for a few seconds , [protect your eyes with safety glasses].
E
Let me know the outcome, if the unit survives a power on period of a few minutes, there is a further TLC job to be done.
EDIT:
If the size of the unit is smallish, use a plastic bucket to immerse the unit in the soapy water.