Defect image display screens are capable of accurately presenting features of defects. Conductive contacts provided on the cover of the PTD are incorporated into a plug assembly mounted on the cover. The heater heats an area on the sheet to which ink is applied by the print head. In a third variant, light with emission wavelength is beamed into the optical waveguide, the optical signals beamed in with excitation wavelength and the light created by stimulated emission detected.