Laney GC 120 busted.

[Kensei]

I have an odd problem with my GC120 And I can't afford to get the only local amp technician to look at it (£60/$100 just to look at it, plus the repair).

It works okay when it's first switched on except the revere appears to do nothing.

After a few minutes the volume dies to almost nothing (below the volume of the guitar acoustically). It happens on both high and low inputs on clean and dirty channels.
I'm guessing master volume pot or thereabouts but i've been in to have a loom and can't find any bad connections.

Any ideas?

Thanks.