Line 6 spider 2 head problem

[Sahe_Bassist]

Hello everyone,
My brother (who plays guitar) has a line 6 spider 2 head and the matching 4x12. The head has two 8 ohm 75 watt outputs (its stereo, 4ohm 150watt when using both outputs). We have noticed a clicking sound when he plays, and a volume drop/rise occasionally. It doesn't happen all the time, but it happens. We have tested all the cords, guitar, foot switch, and have discovered that it is one of the outputs on the head. I think it may be a bad solder joint somewhere (thinking it might be the output jack itself).

Anyone have this happen to them or advise on what to look for after I get this thing taken apart?

[B-string]

You should find a small board that has the output chips inside. Check there for bad solder joints and clean the connector and cables going to it.