SoundLab SP500 Amplifier

Question

I have a SP500 amplifier that needs fixing as a favour for a communial centre, they had put two speakers into one output. Two of the main mosfets blew in the full bridge circuit. I replaced them but only got sound from one channel, but then the other two blew. Is there a special way to set this amp up when replacing the mosfets? I noticed a pot that could be adjusted, but without a circuit diagram I'm stuck. I do have access to test equipment.
Any help appreciated.
Thanks.