I have a 1993 Carvin LB75 that's been sitting in the case for a long time. I took it out the other day and found that it doesn't work anymore. No output. A new battery didn't help so I proceeded to clean the jack with sandpaper and that got it going, but the knobs don't have any effect. It's just always on.
The volume won't go up or down and none of the other knobs have any effect either. It sounds alright but all adjustments have to be made at the amp.
It's the older style Carvin setup (active electronics with four knobs but no switches). The knobs are, Volume - Pan - Bass - Treble.
My knowledge of electronics is limited, but I understand the basics. I can solder, but I don't have a multimeter. Even if I did, I wouldn't know where to start.
Since corrosion was the problem with the jack, I'd guess that it's a problem somewhere else too. That or a loose connection that I overlooked. It doesn't look like anything is burned in there and everything seems intact, though I will take a closer look today in the daylight.
I'm guessing it's not the knobs themselves because none of them work at all and they don't make any of that scratching sound when turned. The Bass knob has a slight scratchy feel to it and I can hear it too (if I put my ear up to it) but I doesn't come through the amp.
Any suggestions about what to look closely at (or test) would be greatly appreciated.
TIA
Jim
Active Bass sends signal, but knobs have no effect 
Update (=nevermind) 
