Emu XL-7 & MP-7 User's Group

forgive me but i'm new. okay, i've suddenly lost sound on tracks 
4, 6, and 8. i don't remember doing anything. i've checked 
evreything i could think of. any ideas on what parameters i 
should be checking to fix it. i can bring up presets and scroll just 
like normal but no audio comes out. i have the volume cranked 
on all channels. i'm thinking that these channels may be set to 
trigger externaly but i can't figure it out. thanks. btw, i'm loving this 
thing. 
-t