English to Polish Tech/Engineering Engineering (general)

It is possible after continuance work and many times of switching on and off the cable's coupling to the jack box the contact between them to be destroyed. There are 2 terminals with sight holes in the jack of the back panel of the device. Put something sharp like a knife or a screwdriver in the sight holes and make them wider. Thus the coupling will fit better into the jack which will improve the contact between them.

(from a metal detector manual)