iMac 27" model 2010 - speaker weird after exchange of logicboard I exchanged the logicboard and now the speakers don't work well. 

If plugged in both on the logicboard then the right speaker (the one without the subwoofer) makes distorted sounds.

If I plug out the other speaker then the right speaker sounds good!!!

Left speaker plug in only: no Sound at all.

I checked the restistance. It is similar on both speakers. Between 1 and 2 pin it is 5 ohm and between 3 and 4 it is 10 ohm. So apparently, all is fine with th speakers itself.

I also tried to reset PRAM and SMC.
My problem was that I accidentally screwed the cable of the left speaker with a screw from the housing. I resolved the issue and sound is okay!