As far as I remember, there is no locking mechanism on the lid. The unit simply detects it going up or down to control the mechanism. If this is a unit that has been in storage or unused, it could have dried damping grease at the two hinges. I would first try using a blow dryer at low setting at the lids back hinge points to soften it. Then try lifting it by both front corners so the upwards pressure is equal.

Yes,you are right. At second tought I remember it also. I did access gearwheels after removing bottomplate.