Hotpoint Aqarius won't spin despite new brushes?

My Hotpoint Aqarius washer/drier had been working ok but then just stopped spinning. I have run a test cycle and everything else was ok (fills, drains, blows hot air etc) but the drum won't turn. I whipped the motor out and swapped the brushes (the ones that came out were very worn). And presto! The drum span - briefly... Anybody have any ideas why it worked briefly with new brushes? I have turned the drum by had and there's no obvious resistance and the belt is in good nick with good tension. I left the top off the machine so I could see the motor and there did appear to be excessive sparking. I am concerned that this is a problem with the motor control. Can anyone suggest a way to test to find out? I'm loathe to pay an engineer to come out! Cheers, Mark