Abstract: A system for inspecting the electronic integrity of solder joints by repetitive pulse-heating the solder joints with radiant energy and determining the temperature oscillation of pulse-heated solder joints by measuring the infrared emissions from the solder joints during heating and non-heating periods. Advantageously, the exposed solder joints of a circuit board can be tested all at one time by pulse-heating the entire circuit board. The temperature oscillation of each joint can be compared to the temperature oscillations of corresponding standard solder joints of known good electronic integrity on properly operating boards.

Abstract: An optical transducer having concentric radiant beam detectors for converting a radiant beam to electrical signals including a first axially placed detector with a second detector concentric therewith. In one embodiment, the detectors receive the radiant beam through an amplifying auxiliary lens. Changes in focus differentially affect the magnitude of the beam impinging on the individual detectors, resulting in corresponding changes in the individual detector outputs.A focusing system employing the transducer moves a focusing lens in response to the differential output of the individual detectors. The focusing system can be employed in a video disc reading system so that the video disc scanning beam is always focused precisely at the disc. An electrical difference circuit leading from the photo-detectors generates a driving signal to energize a lens-moving motor for shifting the focusing lens along the axis of the beam.