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In modern high-power industrial processes, multipulse cycloconverters are fundamental to feed synchronous motors. Given the importance of these critical processes, particularly for mining industry, the reliability of the high-power drive is critical. Having a noninvasive system capable of detecting and isolating faults in the thyristors is quite valuable, and it will reduce the economic losses caused by the long repair times of the converter. Currently, it is difficult and, in some cases, almost impossible to determine which of the SCRs experience an overcurrent or those which do not trigger properly, causing a malfunction. In this paper, we present a new method of online detection which is capable of delivering information about the SCR involved in a failure and the nature of it. This new method takes only a few input and output measurements (noninvasive feature) already available in the most of industrial cycloconverters and performs a timing analysis of these measurements. The algorithms of the method estimate and analyze the switching states of all thyristors, providing an impressive way of detecting the cause and consequences of the failure in the cycloconverter.