i bought a qtron+ about 10 years ago. it’s in the big box with an fx loop. unfortunately it doesn’t really seem to pass signal anymore. or at least it only passes it at very low levels. i’ve replaced jacks & wires (even the trimpot which was just spinning in circles), but the problem persists! furthermore, unless the ‘boost’ is engaged there is no sound unless i crank my amp. with the boost engaged if i turn the gain down everything goes away. i’m guessing that one of the opamps is shot, but i have no idea where to start; there’s 6 of them! my next step is to just start socketing the amps starting with the one closest to the switch, so any guidance would be appreciated.