Using American electronics in Japan

I bought a Gemini CDM-3600 (Dual CD Mixer) in the USA but I've been using it in Japan. The unit is rated at 115v. Japan's power supply is 100v. I've been using it fine for a few months but now there's a buzzing sound coming from the speakers and the unit smells like it's burning.

I was told (by a few non-experts) that there wouldn't be a problem using this in Japan. I emailed Gemini about the problem and this is what they said: Yes it can seem that from 100V to 115V is not too much difference, but the problem is that a difference with voltage means difference with current , and this is the main problem, the transformer is built to work with currents managed at 115V not at 100V.

Lots of US electronic equipment works in Japan without burning. Does anybody know what happened here? If you've had a similiar experience, what do you think the chances of having it repaired are?

Thanks