An encoded serial data bit error analyzer captures the actual waveform of an encoded serial data stream associated with a bit error so that a user may readily validate the cause of the bit error. An encoded serial data stream decoder in the analyzer is modified to provide a signal for a trigger system when a characteristic of a bit error failure is detected. A power splitter produces a pair of incident encoded serial data streams from a programmable test signal, one of which is input to a device under test and the other is input to the analyzer. A re-transmitted encoded serial data stream from the device under test is input to another channel of the analyzer. The encoded serial data stream decoder provides an “error detected” output when a condition occurs in the re-transmitted encoded serial data stream indicative of a bit error. The “error detected” output is used as a trigger signal to capture the incident and re-transmitted encoded serial data waveforms surrounding the detected bit error.