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toy musical keyboard...How to fix?

I am new to Making and to instructables so bear with me. I recently bought an old toy musical keyboard at a garage sale. The nice ladies told me it would work with batteries but of course it does not. This is a no name (brandless) toy probably bought on the street in Hong Kong or something. Anyway, I would eventually like to get into circuit bending and the like but for now I would just like to try to understand how to fix the thing. Does anyone have any advice? Can you point me to a resource on how to troubleshoot this thing? I know I will probably need a multimeter and a soldering gun but other than that I am clueless. Thanks