Increase the volume (4,2)
(Other definitions for turn up that I've seen before include "Increase strength" , "Show" , "part of leg" , "Appear by chance - increase volume" , "surprise" .)
(Other definitions for turnup that I've seen before include "Discover, or make appearance" , "Arrive unannounced" , "Trouser leg end" , "Be found after being lost" , "Arrive (uninvited?)" .)