wma 36 wont drain on end of wash cycle?

Help. My wma36 stops at the end of the wash cycle and displays all lights - wash/rinse&spin/final spin. I checked the pcb and found one of the tracks that outputs to the pump to be burnt out. I got a new (2nd hand) board but it made no difference. The pump works fine as i've hard wired it to the mains with a couple of spade connectors so I can switch it on and off at will to drain the machine. If I time the draining right the machine completes its cycle correctly incl. rinse and fast spin. What causes the pump not to get the signal to drain - I cleaned everything out but to no avail. I have been told by the person that supplied the board to totally remove and discard the ping pong ball. Any suggestions would be great..