Hoover 1300 Special Edition (CA232) Timer Problem?

Hi,
My Hoover CA232 Washing machine has recently started playing up, some programs work fine but normal washes often end up with the timer stopping part way through the cycle just after 4 sometimes you can hear the water still pouring into the machine but the timer does not move, moving the timer on one notch doesn't help at all!
Does anyone know how I can repair this myself? The machine is about 4 years old and mechanically / physically perfect!
Thanks in advance, Linda.