but when the cap dies it should make all kind of weirdo sounds cause the cap is only for filtering, shouldn´t it?

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Normally, yes, but the cap I'm referring to in this case would be in series with the speaker, not a bypass across the power supply. If this cap dies, you get no (or very weak) sound. Now, having said that, I am not at all certain that there is such a cap in this model. I'd promised Stuart Bell to extract a schematic from an analog board he arranged to have delivered, but as with many of my projects, it's for some other day...