from crackles and hum caused by nicks and abrasions in the shielding or cable insulation. Techs also check the batteries on "outboard" devices — effects boxes, tuners, and pre-amps — and wireless transmitters, and change them as necessary. Depending on the size of a band's road crew, the guitar tech may either do this maintenance him- or herself, or, in a large touring act, delegate tasks to more-junior personnel. The guitar tech does a basic soundcheck with the different guitars, amplifiers, and effects, to ensure that the equipment is functioning properly and that all of the connections between the equipment (which are made with patch cords) are plugged in correctly. This may be as simple as plugging an electric guitar into an amplifier or plugging an acoustic guitar into a DI box and preamp/equalizer. On the other hand, a tech may have to set up ten or more electric guitars, a variety of amplifiers, and connect them to an intricate sequence of effects pedals. When all of the instruments and equipment are set up and soundchecked, if there are problems — crackles, hum, no signal from the guitar, no sound from an amplifier — the tech may have responsibility for troubleshooting to determine the cause or causes. Common problems include damaged patch cords, ground loops in connection between instruments and amplifiers, weak batteries in effects boxes or on-board preamps, bad vacuum tubes in tube amplifiers or overdrive effects, broken electrical connectors or solder joints, speaker voice coils damaged from the previous concert, or equipment damaged during transport. Tuning problems may come from old or dirty strings, damaged or worn machine heads or frets, or mis-adjusted bridges. A guitar tech is often a "jack of all trades," expected to make simple repairs: resolder a loose wiring connection inside a guitar, replace an amplifier tube, swap out a damaged speaker for a new one, reglue a loose part on an acoustic guitar, or adjust a truss rod. In cases where there is either not enough time to make the repair, or if the equipment is damaged beyond repair, the guitar tech is may be responsible for finding a replacement instrument or part, either by purchasing or renting it from a local music store or by borrowing it from another band. While another member of the road crew may be dispatched to pick up an item, the tech usually writes down which models