We have an Allen & Heath Qu-7 mixer and two AB168 stage boxes. Last night we had the mixer connected to two AB168 stage boxes in series by S-link cables. The stage box nearest the mixer had two phantom-powered microphones as inputs, and two monitors as outputs. After being powered up for about 3 hours, the AB168 suddenly stopped working (it was still on since it showed the phantom power lights) as it stopped sending to the monitors even though the mixer was sending to the stage box. The AB168 was powered down then up again, and seemed to work for the remaining 1 hour of rehearsal. Does this suggest that the AB168 is failing? It is new, having been purchased 3 weeks ago. Last night was only the second time it was used in a rehearsal.