Yes, I do, but it was in fact the MIDI problem. I think I turned off the ext clock switch before the stop message was sent. I reconnected it, turned ext clock back on, sent the stop again, turned ext clock off, and disconnected the MIDI cable. Works fine now. But there should be some way to do a factory reset.
Did this solution work? I had my 2880 set to use an external clock, and stopped everything, then powered down. Now it won’t respond to anything other than track select and stereo mode — won’t record, won’t play, nothing. How do I send this stop message, given that I think I already did? And is there a way to just reset it to factory defaults?