Robin…
You have given no useful information to help us help you. Please try the following and report back:
1. Check the right speaker to make sure it is working. You can do this by swapping the cables from L to R.
2. Check your speakers by connecting them to the L/R mains out to see if the output is correct prior to assigning L/R to the Alt Out.
3. Tell us what input(s) you are using and from what playback device. Using the channel metering frome the Home>Meters screen, verify that both the input channels and outputs show signal.
4. Use headphones and the PAFL to listen to the incoming and outgoing signals.
Now tell us what is happening with all the derails.