Best thing you can do is follow the tests in the link klerc posted. If you’re getting cracking/static, try moving the low/mid/hi switch around at the back. If you’re going to see it in person before buying, ask the seller if they can leave it on for a few hours before you go to check it out, since the voice chip issue doesn’t always appear until it has been on for a while.

I just got one this month and love it. Unfortunately, voice 2 went out within 48 hours or so of getting it, although it still works occasionally. The voice chips will fail…it isn’t a question of if, only when. Best thing to do really is to get the Analogue Renaissance clones and be done with it, but if you’re not prepared to deal with that, you should look at another synth. For me, it was worth it.