Alesis QS6.2 Output Noise

Hi. I have an otherwise mint condition Alesis QS6.2 that has developed a really annoying hiss / buzz on both main L/R outputs. The noise is so prominent that the board would be unusable except that I found that the noise isn’t present on the “headphone” output, so I’m temporarily using the headphone out to my mixer. However, I’d rather use the regular main outs… Any idea what is causing the loud hiss / buzz? Any idea how to repair?

Thanks in advance for any help you can provide.

Just noticed this… the hiss / buzz is actually on the headphone output as well, but the output level on the headphone output is significantly higher than the mains, making the “signal-to-noise” better and the output more useable. So the source of the hiss / buzz noise is probably upstream of the individual output sections…