Protect light

I have a Mackie HR624 Active monitor. I have been unable to find a schematic. My protect light on one of them stays lit for the first 5 minutes after they are powered up and will fade on and off regardless of whether signal is being applied. The sound is not significantly affect relative to the illumination. The same monitors have a power on issue with age. Would this overload circuit be affected by sagging power supply caps? Where can I learn about protect circuits?