Alesis RA500 Service Manual [URL="http://www.audiosmile.com/forum/Manual/Alesis-RA500.pdf"]www.audiosmile.com/forum/Manual/Alesis-RA500.pdf[/URL] It seems the relay that switches the speaker connections on with start-up is a common fault with the RA150, RA300 and RA500. If the amp powers up but you don't hear a click, or one of the channels just doesn't work or sounds distorted but the fault is intermittent, this could be the cause. A simple check is to tap the relay with the end of a screwdriver and see if the fault changes at all. I've found a suitable replacement for the Dong Woo DW321-D12S relay is the 'Finder 44.62 - 10A 12V DPDT' relay.