Hey folks, I have a Mackie 802-VLZ4 mixer which does this narsty pop when you turn it on; I'm pretty sure it's what killed one of the woofers in my monitors. It has been put out of service and I will either harvest its many through-hole organs or else fix it.
I could not find a schematic, but I don't assume it can't be found, I just haven't yet. It's not a big board but it's all analog from what I can see.
There appears to be a separate power supply board which feeds
+15 AGND -15 GND +48
to the mixer, which is two boards connected by thick soldered wires.
I have looked with magnifiers on at all the caps, none appear to be leaky or swole, but I'm assuming this has something to do with the power supply putting out a spike at power on. The power board has a lot of really tiny caps, I still don't really understand power supplies that well. I need to do more studying of them I suppose, they're pretty central.
Edit: I have a little tiny oscilloscope that I bought years ago and haven't used yet, just figured the day would come. This is probably that day, to measure that spike from the power supply. From the looks of it I'm pretty sure that if I can just get better quality, non-spiking power to those connectors it should be fine.
Anyways this board would be very handy right this second if I felt like it was safe to let it touch my good kids, but at the moment it's the unfavored child who won't stop hitting the others. If anyone would like to see them I have/can take photos. The boards have codes on them, presumably codes that Mackie employees could use to dig up schematics, but will they? I suppose I'll try to find out today. It's past warranty of course.
There are timing relays for under $50 that can delay the power to the amps for a few seconds. You just need to buy a 230V model (for input and switch) that has the current capacity for your sound system.