Yamaha GO46 speaker connection

[bella vita]

I'm new to this forum. Thank you in advance for any advice you may have. Please pardon me if this is a silly question.

 

I'm not succeeding in getting sound to both speakers, channelled through my Yamaha GO46 audio interface. I bought this interface, used. When I connect a cable (phone jack and two RCA jacks) to the output in the rear (I've tried outputs 1, 2, 3 and 4) and to my speakers (Edirol MA-15D monitor), I get sound only from the left speaker. Attaching my headphones (Sony MDR-CD900ST) properly to the same 4 outputs produces the same results; however, sliding the headphone jack in only partially does give me stereo (but the slightest touch destroys the connection). That trick doesn't work at all, though, with my speaker cable. I would've thought it was a defective cable, but the same thing (sound on the left side only) happens with my earphones.

 

On the other hand, connecting a (different) cable directly from my computer (MacBook) headphone output to the same RCA inputs mentioned above successfully gives me stereo. So I know the speaker inputs are okay. (I can also connect the MacBook to the single 1/8" input on the speakers, and that works, too.)

 

Innoccent guesses: Is it possible that there're more than one kind of 1/4" phone jack? I can't imagine that all four outputs on my audio interface are damaged. Or could it be possible that the previous owner used the software for the GO46 to change some setting that needs to be changed back? (I don't use or even have the software, although I imagine it's available on the net.)

 

Any ideas greatly appreciated!