Mackie CR3 bookshelf speakers only play incredibly quietly on max volume

Question

I've got a set of Mackie CR3s which the company sent to me when I warrantied my purchased set whose L/R selector corroded (was able to save that set by removing the component and hard-wiring).

The set they sent worked great for a few days, but I'm worried some direct sunlight heated them up too much (speculation) and now they only play incredibly quietly when on max-volume. Here's a video showcasing the problem.

I've tried different input sources, cables, switching L/R and only running the active speaker.

My electrical engineering skills are pretty limited but I'd love to learn and fix these if possible.

Thanks in advance for any help!

Answer 1

This is a standard issue diagnostic issue. We could send you to an audio equipment SE but diagnosing issues is what I do for a living.

You say you have already checked most of these but the order I'd check things would be:

1. Is the output volume from the phone at max level? When you have multiple volume controls, the simplest solution is to set the upstream outputs to max and control from the last in line. (It's always embarrassing when that is the problem.)
2. Do you have another source of audio? Try plugging your cable into a friend's phone and see if that changes anything.
3. Do you have another cable? This is not symptomatic of a cable problem but it should be easy to check.
4. What happens if you plug the cables and power source into another speaker? (Test the test equipment.)
5. If you plug earphones into the earphone jack, does the volume act the same way? How about the aux?
6. As @DKNguyen suggested operate all switches and controls to make sure there is no corrosion. Sometimes, just cranking the volume up and down and clicking all the switches on and off a few times will make all the difference. I see there are jacks for earphones and aux(?). Try plugging a cable into the jacks a few times to check for corrosion there, as well. You said these are "new" replacement units? Corrosion is less common for something new but if the vendor had them lying around, it could happen.

If you got this far, you can open up the case and look inside... but they are sort of new. Opening the case voids the warranty most of the time. As is, the speakers are of "limited value." If the vendor is not going to help, the choice becomes opening and junking. I'll go with opening every time, occasionally, I even fix things that way. Keep in mind that if it starts working again, it needs to go together again.

0. DISCONNECT THE POWER. Don't just turn it off, unplug. If you zap yourself, I don't know about it. Watch out for the power supply, they commonly have capacitors that can hold a charge.
1. The most easiest way things get fixed by opening is by replugging all the cables and other connections to resolve any potential corrosion issues.
2. It was in the sun? Inspect the drivers (the speakers inside that actually make the noise) to see if glue separated or something. This is not symptomatic of that but it's something to check.
3. Low volume? If it were very slightly shorted out inside somehow, the short would load down the input and so the amp would think the signal is low. This is very unlikely but check closely for anything that does not look like it should belong.
4. Now for the actual electronics... that will require test equipment that I'll speculate you don't have. If it was open in front of me, I'd have all kinds of ideas on things to check but without seeing it, I'm kind of out of ideas.