Abstract: Error detection for digital television equipment that strips away the vertical and horizontal intervals of a digital video signal so that only the active picture portion of the digital video signal is determined by a digital test signal generated from the digital video signal. The digital test signal has replaced at a predetermined location in the active picture portion of the digital video signal one or more video data words with data values that represent check word data for the active picture portion. The check word data may be inserted into the beginning of one of the horizontal lines of the active picture portion of the next field, or may be modified and inserted into the end of the last line of the active picture portion of the same field of the digital video signal. A receiving instrument processes the output of the digital television instrument under test to generate active picture check word data.