Troubleshooting Circuit Boards within the Digital Correlator of the Smithsonian Submillimeter Array

The Smithsonian Submillimeter Array, on the summit of Mauna Kea, Hawaii, includes eight antenna dishes and a digital correlator back-end — a large array of electronics that amplifies incoming signals and reduces noise by comparing those signals between pairs of antennas. Each correlator is responsible for relaying, digitizing, and down-converting incoming signals from approximately 200 GHz to 1 GHz, and consists of a series of large processor circuit boards loaded onto steel racks (or “crates”) of six circuit boards each. Given the large number of individual circuit boards, a systematic approach is needed to diagnose and repair boards as they fail. The troubleshooting begins with analyzing the output signal through terminal. Once the problem is detected, schematics point to which chips may be responsible for that particular problem. Suspect chips are removed, replaced and the board is then tested to determine functionality. By studying common failure modes and effective repair strategies, we have developed a three-step troubleshooting method: analyze the board’s output signal using a terminal, use schematics to find and replace the failed component and test the repaired board for functionality. So far, four receiver boards have been successfully repaired with this method. Because of the complexity of the correlation process, keeping track of past failure modes and successful repair steps is essential for troubleshooting boards efficiently in the future. Once a number of the repaired boards’ and their malfunctions have been documented, a troubleshooting flowchart will be constructed as a clear guide to assist future correlator technicians.