Mackie CR1604 that has been rack mounted in the studio since day one. Developed a mysterious intermittent snap across the main output, only occurring once every few days. The sound did not happen when on the repair bench at "Backline Musical Services" so they were unable to isolate the issue. The unit is in otherwise great shape so lots of parts OR if you're talented with electronics this could be a killer deal on a great board. Sold as is, thanks for looking...