I'm into electronics, so I went looking myself... but the circuit is potted in epoxy which makes is next to impossible to work on.
The motor drive electronics has two sections - one for each direction of motor rotation. In one section a resistor had cracked and I only found it through careful observation and a lot of luck.
I dug through the epoxy and managed to fit a replacement component (10 cents worth!). It was not easy and the whole unit could have been wrecked - but I had an exact spot to target and my time was my own.
Don't even suggest this idea to a professional service guy. It would take too long and the outcome would not be certain - he wouldn't guarantee it in any way. These things were meant to be field replacements. Just get a whole new board.
The result was not pretty - but it has been working flawlessly for over 4 years now.
WARNING: If you have no experience, DON'T DO THIS!! LETHAL voltages are involved - and you're playing around in a wet area!
Michael
April 2010