Percussive engineering - brilliant!
When I was learning to fly the Jet Provost, on one occasion an AC inverter wouldn't start as advertised. The groundcrew lad raced off to the hangar, from which emerged a grizzled old Chief in one of those brown pigman's coats they used to wear.
The next thing I knew was the nose had been opened, 'Chiefy' then rolled up his sleeve and reached inside - and the aeroplane shook as he thumped the recalcitrant inverter in the nether regions, whereupon it started working. Down with the nose, thumb up and off he went. No paperwork, but job done!