Frigidaire washer won't agitate

This is a stacked unit w/d. The washer will fill then stop and proceed no further. If I advance the timer to the spin cycle it will spin and empty. During any of the agitation portions of the cycle the timer will not advance nor will it agitate. The lid switch works as it will spin with the lid closed. It seems to fill to the desired level. A troubleshooting guide I saw said it could be the timer and it could be that the motor is burnt out in one rotation direction (the agitate direction) while the spin direction is operational. How can I determine what I should replace? I would like to be certain before I take the plunge in either of these expensive parts. Help!