My Philips Whirlpool 1100 AWG 750 Will only spin on half load?

My Philips Whirlpool works perfectly on any programme, washing, emptying, rinsing and spinning etc, until it reaches the final spin cycle. It then just stops. Through trial and error, I have discovered that if I remove half of the weight of the load, reset the programme dial to [A] which is a short rinse and spin cycle, the machine refills, rinses,spins and switches off. I am using the correct load and This procedure works every time. Why will it not complete the programme on a full load.
Anyone who can help, thank you in anticipation.