Hey guys! I picked up a MIA 4Pro last week for $300. The only problem is that power amp A does not work (mono bridge does not work as well). Power amp B works great! I have read old forums on problems very similar to this with the 4Pro. I have tried contact cleaner and inserting instrument cables in all of the jacks. I have played with all the buttons to see if that was the problem. Nope. Still no sound! So... I am wondering where to go from here. Should I send it back to Ampeg to see if they can fix/replace the power amp or is that too expensive? I have a tech but he specializes in tube amps. I'm not too sure about his knowledge on mosfet power amps... I'm just looking for someone who has been in a similar situation and what you did to resolve the problem. Thank you all and have a great day! GO SHARKS! *Sidenote: There are no certified Ampeg service centers in the SF Bay Area.