How do I repair the motor of an Ecectrolux Vitesse bagless cleaner?

When the cleaner is switched on there is a big flash of sparks where the brushes of the electric motor contact the commutator and the motor runs for a few seconds and then stops. If the motor is then switched off for a short while and then switched on again the same thing happens. There is what looks like a condenser wired between the two brushes - has this failed or has something else failed.