NealEC

Decent, but I have another theory, (or variant on your loose grounding theory! Mine is a Mackie CFX12 10x I checked the on and off for every solo button, all up, still red light going. Enter the internet, and a post warning about plugging 1/4 inch mono cables into the inserts. Well, the last known thing to happen was on my 8th fader which is 11/12, and the insert doubles as a separate 1/4 inch input; I mean at times we have jammed with 4 guitars, 2 in each of those... no problems since like 2005. Well, last Saturday, (Nov. 2022) I tried to watch tv, with the "tape in" audio coming from my tv... I turned on the mixer, and had the rude solo-light-same headache discussed above, except no way to get any sound out of mains monitors, headphones, auxiliary--nothing, no joy at all. After reading a bit on line, I tested my theory that maybe this mixer is not garbage yet, I pushed stereo, and mono 14/males in and out of the inserts. No luck at first. Then I thought the last one used is likely the one I ought really concentrate on. It turns out on mine, the problem was something in the 12th line right 1/4 inch jack, (maybe some tired metal got bent and shorted, maybe whatever). Multiple penetrations w stereo and mono typical patch chords with PA on, but no speakers attached to make noise--suddenly rude light stopped blinking. I plugged in the speakers, and tested stuff out and I'm back up. I put masking tape over the inserts, as it is not uncommon for folks at a jam to mindlessly shove their patch chord wherever, and isolating a problem on a mixer is really time consuming process I do not want to endure again. Strange, but meh everything wears out I guess... just thought sharing might help someone else too. I got her working again for now, and this might not be your problem, but trying this is way easier than removing screws, and opening up pandora's box. Hope this helps someone else too.