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Mixer makes loud pop when powered on (self.askelectronics)

submitted 1 year ago* (last edited 1 year ago) by JTode to c/[email protected]

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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.

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[–] [email protected] 4 points 1 year ago

Hi there,

Based on the experience I gathered in repair cafes:

Some old power switches generate an arc (spark?) when flipping them. Cleaning their insides with an "electrical contact cleaner" spray can sometimes help.
Defective electrochemical capacitors do NOT always swell or leak. If it is worth it swap them all for new ones (We sometimes desolder what we think are good ones from dead appliances to be re-used).
All domestic appliances around here (France) have an "anti surge" (?) capacitor soldered just after the power cable and power switch. If I understand it correctly, its job is to prevent a "parasitic" current spike to travel back on the domestic electric network when the equipment is switched on. That's the one I would replace in priority to see if it fixes your problem.

Disclaimer : I have no degree in electronics / electrical installations. Take what is above with a grain a salt as I might be dead wrong.
Always unplug the appliance from the mains before tinkering and discharge ALL the capacitors which are on the 110 V /220 V side of the electronics before touching the PCB on which they are soldered.

Good luck with your repair. It would be nice and helpful if you have a chance to post some pictures :)