K5synth

I just got my K5m from eBay. It is cosmetically in a good shape.

LCD Backlight is almost dead but the screen is still readable. I have another small issue though that I would like to address first. 

Here it is.

I noticed when MULTI is selected and a SINGLE patch is routed to the discrete output # 3, I hear no sound at all. But when SINGLE is selected, this output works fine. Other outputs 1, 2 and 4 work fine with either SINGLE or MULTI.

Any hint will be appreciated.
Thanks,
Christian