EBS Fan

I have a Reidmar 740 bass head and a Drome Classic. With both amps I can't get the Gain light to respond to set the initial level for the amp. I have tried turning the Gain control fully up and the bass fully up, G&L L2500 Tribute, but no response whatsoever from the Gain light. Has anyone encountered this before.?Any clues as to what might be wrong ? .