Abstract: A diagnostic instrument (10) for testing the functioning of an infrared radiation emitter (14) contained within a VCR (12) or other electrical equipment is disclosed. The instrument (10) comprises a housing (16) and an electronic circuit received within the housing (16) for detecting the presence of infrared radiation. The electronic circuit comprises a battery (26) or other DC power source electrically connected in series with an infrared sensitive photodetector (22) and a status LED (24) which is illuminated when the photodetector (22) is exposed to infrared radiation produced by the emitter (14). A switch (18) is provided for selectively turning the instrument (10) on and off. A battery condition LED (20) is also provided.