Ahhh....Sweet sweet success.

As mentioned above, I suspected triac 105 (Agitate triac) was "latching up" which is a common failure mode of triacs. They turn on when they are supposed to, but won't turn off until power is completely removed. Thus the washer would agitate, but never switch into a drain cycle (even when the controller signalled the triac to turn off. Since the controller board never saw an "empty" signal from the water level switch, it would agitate forever, or at least until I turned the washer off.

I ordered a triac from Mouser Electronics for 32 cents, and it took just a few minutes to unsolder the old one and solder in the new one. It just ran a complete "Gentle" cycle start to finish, which matched the timing diagram exactly.

Gene, thank you for your reassurance and help. Without it I would have spent way too much time on mechanical stuff.

By the way, I couldn't match the part number of the 23-year-old part, so I just bought a way-overrated part in the same TO-92 package style as the orginal Motorola part. I suspect a 1-amp 125 or 150 volt part would have worked, but the 800-volt, 1-amp part was only a few pennies more. I got a ST Microelectronics 511-Z0103NA5AL2.

Larry Marks
Computer electronics engineer for the last 39 years.

Whirlpool belt-drive won't spin when it's supposed to and i don't know what to do