fwiw - for my Mackie CR3s: The two big power supply smoothing caps - the 4700uF caps, C76 & C77, were obviously bad as they were bulging. And no surprise given the heat the power supply generates, esp as it's enclosed inside an insulated speaker box. So I replaced those; but that still didn't fix it. I still had bad voltage readings. I then replaced the two regulator zenier diodes, Z3 & Z4. That did the trick and all is currently working fine. I'll probably modify the powered speaker to leave the electronics outside the speaker box so the heat can better dissipate. There are 'proper' fixes out on the internet that involve bypassing the original power supply regulation section with LM-series voltage regulators. Those fixes will significantly reduce the heat produced, which should help with longevity.
Also fwiw - on the MUTE issue re the mute pin on the TDA7265: It has been noted that inside that chip the mute function also performs a voltage safety check; so ideally you shouldn't fix the mute issue by simply cutting that pin. The mute circuitry is voltage dependent. If the mute failure isn't fixed by cleaning the headphone contact; then you probably have failing caps and diodes. C76 & C77 should probably just be replaced ever few years anyway as they take a beating. Replace those, then Z3 and Z4. If that doesn't fix it, replace the capacator and diode in the mute circutry - C74 and D1. NOTE that I myself am not an electronic circut expert; I am here consolidating a bunch of research I've found across the internet.