KitchenAid runs, washes, won't drain

Trusty old Kitchen Aid that doesn’t get used more than 1/week has now stopped draining. It runs through the whole was cycle OK. I’ve replaced the solenoid valve cause someone at this expert-advice place said I needed to–and he’d be willing to sell me just the part! Motor runs, all drain lines downstream from the motor/pump check out clean. No food/debris apparent. Any suggestions? (I’m an electronics teacher, so give it to me with both barrels.)
Bruce

NEWSFLASH–The owner of this Kitchen Aid breathlessly reports that he just tried turning the dial to the area he guessed was close to DRAIN and the machine drained just fine, fast and fine! So it CAN drain, but it DOESN’T drain when left to run through its cycle. Hmmm. Bad timer?
–Bruce Ratcliffe