imac G3/600SE speakers suddenly distorted sound output

This computer was only randomly used and did run perfectly since 2001. The last time I used it to listen to an audio CD was three month ago. Now I powered the 'flower power' imac up again trying to listen to some itunes recordings, but there is a very low level sound and when turned up to slightly higher volume it immediately distorts in the peak levels. To conclude the volume is very soft, but in volume peaks it heavily distorts. The headphone output is also only very low level, but with some less distortion. I suspect a broken/leaking electrolytic capacitor in the audio power amp circuit. Is there anywhere a schematic available? Otherwise I will pull and measure the internal resistance of the obvious capacitors one by one to replace them when necessary. I will let everybody know here, when I found the problem.