1604-VLZ3, how to fix a non-functioning Gain knob?

[Skeletron]

I just picked up a Mackie 1604 VLZ3 and the Gain knob for channel 9 is completely non-functional. Turning it up does not alter the sound at all. It's a shame because I'm really happy with the mixer otherwise. It's perfect for my setup. The Gain knobs for all the other channels work great except for Channel 1 which is a little scratchy.Is this a problem that can be fixed? I've read good things about DeOxit but mostly for fixing scratchy pots. The fact that the knob does absolutely nothing makes me thing it's a bigger problem, but I have no idea. Does anyone have experience with this? I'd appreciate any help.

[Greg C.]

I've learned years ago to never buy used Mackie mixers. Always problems. Once a pot is scratchy or a button intermittent, they must be replaced. The trim that's broken on channel 9 likely has no ground connection which will cause it to go full gain. So it either a bad solder joint or the pot is broken. You'll have to disassemble to check. If it's soldered well, it needs replacement. Repair of Mackie mixers is a pain due to the cheap large PCB design so they require that you remove every jack and pot nut to disassemble. Have fun. You can order replacement parts at (800) 258-6883 x1623.

[Skeletron]

Thanks! I've been looking all over for people with a similar problem and I found this thread: http://homerecording.com/bbs/equipment-forums/other-equipment-reviews/mackie-cr1604vlz-troubles-please-help-166131/

Apparently these models have crappy ribbon cables that can cause problems over time. To fix it this guy just opened the mixer, reseated the ribbon cable connectors, and that fixed the dead gain pots. Hopefully I can just do the same. :|

[Albundagus]

I just repaired the exact same problem with a CR 1604 VLZ PRO. I checked the ribbon cables, the trim pot and op-amp in the preamp section to no avail. In one of the forums I was looking at, someone mentioned the grounding of the pot. As I was running the traces, the plug J2 on the preamp board (JACK PANEL) at pins 29,27, and 25 (the ground pins for the Trim for CH9) on the back side (where the solder points are) you will see a trace from one of the pins to a solder point. The trace is almost at the edge make sure there are no breaks in that trace, if there is, just solder a wire from that pin to the solder point, then your trim should start working. All the above pins mentioned are tied together to the one pin that is connected to that trace.

The board had a little place missing and it was easy to overlook.