I have an old Presonus 16.4.2 analog audio mixer. It works a bit for about 30min, and then all lights stay on and a high pitched sound goes to all audio outputs. There are also a few channels that are scratchy sounding and channel 12 no longer works. I assume bad internal capacitors are the issue, but if you are good at repairing and cleaning electronic components, or need parts, this could be a good fit. (Free)