You mean TRACK 4, I assume...
Try cleaning the heads. The track widths on those machines are really, really tiny, so any little bit of oxide or other foreign residue can and will wreak havoc on signals you're trying to get to the tape. Often just a quick pass with a cleaning swab and 90% + isopropyl alcohol will do the trick. Demagnetizing isn't a bad idea, either. Do you do this regularly?
Try a different tape. (?)
The heads may also need to be aligned, though I'd say try cleaning first before you pack up & ship out your 488mkII.
Bruce in Korea