Tascam 688 dead channel

[AnalogDigital]

I have a Tascam 688 that won't record to or playback from track 8. Group 8 does not get any signal, either, which leads me to suspect that it is a problem with grp. 8 on the mixer, and not the heads. Also, the Store/Copy key seems to be completely unresponsive, and thus I cannot save my scene settings. Any help would be greatly appreciated.

 

[Peck]

I'm having a similar problem with mine. One channel won't pass a a mic signal.
Then another channel won't pass a line signal.
Pain in the ass.