A method and an arrangement for optimizing the luminance characteristic curve for a display system using a lookup table. The incoming telephone reception signal, which contains both voice and frequency-shift keyed signal components, is processed, e. Since the demultiplexer is to sample the data currents corresponding to N data lines during a horizontal period when performing 1:N demultiplexing, the data current corresponding to one data line is to be sampled during a 1N horizontal period. The degradable locking member selectively retains the sleeve in the open configuration.