Smoke Problem with MTH Hiawatha 20-3438-1E

Gents

20-3438-1E MTH Hiawatha.

Purchased this set NIB recently.  All has been working well.  The smoke fan motor quit.

I went inside, checked all connections, unplugged and re-plugged connectors.

Tested the motor (dis-connected first) with 5 V DC and the fan motor worked.

Just to be sure I replaced the fan motor with an identical MTH smoke fan motor and it tests good as well.

However, when all is assembled and I use DCS to activate the smoke .....the resistors are working but not the fan motor.

Not sure what my next step should be.  Appreciate any help Gents.

Thanks

Dave