Repairing a Janome 9500?

I have had this machine about 10 years from new. I have used it only about ten times. I used it recently and came up with " thread jam, fabric too thick or change needle". I checked and still no luck. I took it to a shop and was told the motor was worn out and I needed a new motor. I did that and it is still not working. Now they say I need a new motherboard for £300.00. Any ideas? Can I buy a motherboard and fit it myself? Thanks for any help.