I have a deluxe Power drift and am having issues with the audio. You can hear music but no sound effects. both speakers are playing music just nothing in the means of sound effects.
Did you try hitting the test button and going through the sound/memory test stuff? From memory I think you can test the roms and amp in there somewhere, I do remember that you can soundtest all the SFX & music. Obviously won't fix it, but might help you narrow things down a bit.
Well, I'll be honest - I'm pretty much out of my depth already. But if its any help (and in the absence of any other suggestions) if it were my machine I'd start by cleaning/reseating the 4 sound ROM's (they're shown in the manual) and if they're OK maybe be thinking one of the sound chips might be bad?
According to the Y-Board specs I have, it has a Z80 sound CPU and then YM2151 & SegaPCM sound chips. If one chip controls the music and the other the speech/SFX (the SegaPCM I guess?), if that was bad it might explain why you have music but no sounds.
But thats the total guesswork of someone who bought a Power Drift last week and spent a couple of days reading up on it - so its not exactly based on years of experience and I wouldn't be at all surprised if I'm completely wrong . But thats what I'd check anyway...