Ampeg SVT 4 Pro distorting...Help!

[PauBass]

At band practice the other night my SVT 4 Pro stopped working, well it didn't stop, the sound volume dropped and distortion was coming through instead of clean tone.
I use the Ampeg in mono bridge mode with the right cable, it's not the cab as I tried it with another amp and it worked fine.

I tried the two power amps separately and I found the problem lies on power amp A, B works fine but A is the one not pumping enough volume and distorting.

Any ideas?

[DanRJBrasil]

looks like a tech time for the svt 4, I am not a tech but obviously seems that you have a prob in the pamp A