I am repairing a Line 6 AX2 212 amp for a customer in our stereo repair shop.  It makes a loud popping sound when the buttons are pressed (esp. user preset).  I am strongly suspecting the mainboard, how can I order one?  Or maybe there is another fix- I reset the memory to factory defaults and it worked ok for about 2 hrs, then started up again.  Power supply seems ok.

Thanks for any help offered.

Jeff