Just a wild guess -- hit F8, the mute button. Maybe the decoder has been muted. If that doesn't help, you may have a bad decoder.
I know this is no consolation at this point in time, but I always test a decoder before installation.
Well, this is frustrating for me. I am trying to install a older Soundtraxx DSD in my Spectrum 2-8-0. I know it's not Tsunami or anything.... Even so, I have one of the QSI speakers for it, and have modified the tender to fit the decoder. So, if I just plug the decoder in it will run the lights and motor just fine, and even though I've heard these have some buzz to them, it isn't evident on this engine. But, I get no sound. I wired the whole thing correctly according to the instructions, with the capacitor, but no go.
What would be the reason for this? Did I get a bad speaker, since the decoder seems to be working?