the disclosure describes a device for locating faults in a working storage arranged in rows and columns . the device includes an auxiliary storage which holds a sequence of test words and means for cyclically writing the test words into the working storage and reading the test words out of the working storage . a bit for bit word comparator compares the words read out of the working storage with the words read into the working storage and detects bits of the words which do not match in order to identify defective components . first and second registers record the row and the column to which the defective component belongs .