Mackie PPM 1008 Mixer section

[HDSarge]

Does anyone have a schematic of the mixer section of a Mackie PPM1008? I have the power amp and SMPS, but with those repaired, Ch3 is very noisy (static) somewhere before the insert jack. The circuitry of CH 3 from XLR to insert would be a big help.
Happy Thanksgiving to all.

[Jazz P Bass]

Mackie PPM1008 Preamp

Happy Thanksgiving.

[HDSarge]

Thanks Jazz. D42 a signal limit diode going to Q33 was the noise maker......without the layout you provided, I would have pulled the pcb with the XLR's and Insert Jacks looking for the mic pre parts. You saved me time, mentally and mechanically; how nice is that!

[Jazz P Bass]

Awesome!

[g1]

I'm not sure if it's some weird Mackie thing, or just coincidence, but I've seen and read of more of these protection diodes causing noise issues in Mackie mixers. Same type thing where you have reverse biased diodes between signal line and +/- supply rails.
One CR1604 I worked on had a half dozen noisy channels, the diodes measured fine but disconnecting them removed the noise. Replacement cured the problem.
Enzo mentioned it could have been dirt/contamination on the diodes, either way (dirt or defect) it's something to check when tracking down difficult noisy channel issues.