Mackie CFX making a popping noise. Also strange fader/channel strip behaviour.

[genekrupa]

It's my new scope that's under warranty - I thought I was doing something daft so I just asked in this thread expecting to hear "check setting xyz".
The Mackie desk is well out of warranty though, probably about 16 years old.

[Enzo]

Oh, like my dates...

[genekrupa]

Oh, like my dates...

I'm no expert but I certainly wouldn't be eating fruit after a few months, let alone 16 years

[Enzo]

Oh, no, I am a healthy hetero...

[genekrupa]

and here was me thinking you were talking about the food

Anything else you reckon I should test on the mixer? Trying to keep this thread vaguely on topic before it gets moved to an entirely unrelated section of the forum

[Enzo]

Well, you didn't bite on post #6, so what else could I do?


We spent entirely too much time on ribbon cables, which are problematic in some Mackies, otherwise we have to work to isolate the noise source. if it is riding on the power supply rail or rails, we have to determine if it is just affecting the PS or if the PS is the cause. beyond that, we have to try to refine our search to find the noise source stage by stage. Anything specific? No.

[genekrupa]

Ah I forgot my username so I just thought 'flam' was some sort of weird typo! You threw me off with the drum puns on a electronics forum! Going to have to resist the urge to shuffle daft puns in now.

I didn't see anything wrong when I tested the power supply earlier so I'm inclined to think that the problem is outside of the power supply, though I'm not sure what the next step is other than "test random things on the master section on the mainboard in the hopes of stumbling upon the problem"

[Enzo]

You scope each power rail, and see if when the thing pops, do you see a glitch on the power supply?

The signal path is indeed a path, the signal enters a section at one point, and proceed stage by stage through the section. So we scope the signal path, and see how far back the pop still appears. We start at the output where we know it is, then step back stage by stage looking for the noise signal. When you find a point where the noise exists after, but not before, you know you are close to the source.

and of course we need to eliminate outside influences. Does it pop at other locations? Does it pop moving it around the house? Tune an AM radio, preferably one on batteries, to an unused frequency, and turn it up, so all you hear is white noise. Now when the mixer pops, do you also hear a pop or something in the radio? That would point to external noise.

[genekrupa]

Yeah, I scoped it while it was popping and posted earlier in the thread - didn't see anything though just fairly clean DC.

I tested it on a couple of different mains circuits, one including a surge protector, and didn't see any change. The fact that I can speed up/slow down the popping by a large amount makes me think the problem is originating from inside the mixer somewhere.

[Enzo]

OK, if it isn't part of the PS or riding on the PS, then move to the signal path exploration.

[genekrupa]

Thought I'd post to update the thread:
I had a poke about in the signal path but was getting a bit lost and still couldn't find the source of the problem.
It looked like I wasn't going to be finding the fault anytime soon, let alone repairing it, so I just admitted defeat and sold it for spares/repairs. Would have been nice if I'd been able to get it sorted but at least I don't have to keep looking at it all the time!
Thanks for all your help anyway.