Why does the XTBM display FAIL SELF TEST in certain receptacles?
The XTBM self-test verifies the signal amplitude and data pattern of its repeater check transmission. It takes several seconds after the XTBM powers up for its digital filters to adjust to the background noise level at that receptacle. Rather than make people wait for that process to complete, the XTBM performs its repeater check as soon as it powers up, using the default values that are pre-loaded into the digital filters. That works well for most receptacles, but a significant noise source or severe signal sucker on the same circuit may cause the read back of the transmitted signal to be out of tolerance, resulting in the failure indication. Loosening up the limits could prevent this, but that would result in the self-test checking just functionality, and not accuracy.
