So channel A is busted.By removing the fuse you also shutdown the excessive current going to the A channel.That is one of the advantages of a switching power supply,it will go into protect mode when the current is too high.If it would have a regular power supply the fuse would just blow every time.
Now my guess is that one or more power mosfets are shot.Usually if one fails it takes the rest out too.And in some cases also the drivers.So best thing to do is replace them all,so both the drivers as the power mosfets.
So that means Q2 to Q9.DON'T skip out on one.Replace them ALL.
Q2,Q4,Q5 MPS8099 0.5$/piece
Q3 MPS 8599 seems to be obsolete but you should find them on ebay.
Q6,Q7 IRF 9530 3.50$/piece
Q8,Q9 IRF 530 3.30$/piece
Found these on the mouser website.So it will cost like 16$ to repair.Not the end of the world IMO.