Genesis 3 without stereo sound?

[Slor]

It is rumored that some of the Genesis 3 consoles were built without stereo sound.  Can anyone verify this?  If so, is there a way you can easily tell looking inside the unit whether or not it should have stereo output?  I recently got ahold of a model 3 and a stereo cable, and I'm only getting sound from the left channel.  I'd like to know for sure if I there is something wrong with the unit or cable or if I simply have a mono unit.  If it helps, the board layout in mine has the main chip turned at a 45 degree angle to all the others.

Also, if it is truly the case that my machine only has mono sound, is there a mod to convert it to stereo?

Thanks for any help!
Slor