Ariston AV1247C will not final spin

Machine runs through the wash cycle, pumps out the water and turns during the spin programme, but does not pick up speed. It seems to start to pick up then looses it again. Brushes replaced about 2 months ago. Have had the back off, belt seems okay, not slipping or anything. Checked the pressure vessel and the surrounding tubes, also checked the outlet pump, everything seems fine. Took out the motor and checked the brushes, just in case. Seemed okay but rubbed over with light abrasive paper and cleaned the commutator with same. Checked all connections and ran the motor out of the machine. Once again the motor spins at regular speed then just as it takes off to speed up for the spin I get a blue flash and it drops down again. I’m baffled??? Any ideas?.