The spring, if I remember correctly, rests on a "shelf"-like piece of plastic protruding from the cast plastic chassis.
If the edge of the shelf has become rounded, the spring will slip off. Everytime the spring slips off, the rounding will be smoother
and the problem worse.
I seem to remember that it's not very hard to grind it back to flat again, you may even be able to introduce a bit of inwards
slope to help keep the spring seated. Maybe a hobbyknife or similar will ease the task.
As an alternative, you could drill a hole and horizontally mount a screw with a fairly large head. The spring can then rest on
the screws stem and the head will block the spring from falling off the end of the screw.

Make sure to get the other end of the spring on to the tiny slider that rides in the groove at the "neck" of the hinge piece.
If you cannot find the tiny black slider piece, it will have fallen down into the Beocenter and can usually be found somewhere around
the large transformer, presumably caught in kilopoise grease from the lid mech.

Martin

The spring on my unit rests in a metal, I'm assuming it is aluminum, casting with a groove machined in it, and is held in place by a metal stepped cap piece held in place by two small screws.  Two larger screws, with washers, hold the spring and cover hinge in position.  Now, is the slider piece you are referring to something that fits onto the loop end of the spring which then rides in the grooved black plastic piece on the side of the hinge, meaning there should be plastic to plastic contact and not the spring loop in the hinge groove alone?  This would explain why it keeps popping out.  Hmmm, I guess I will have to go fishing around the transformer.

Thanks

Steve

Martin,

I have the 7700 open as well as my spare 7000, and the spring on the 7000 has a tiny slider piece that appears to be held in place by that super sticky grease.  It must have a better way of being attached?  I also found a sickle shaped piece of plastic with a loop in one end.  It was laying next to the transformer.  I'm not sure what this does but it has a little post that I think the spring hooks on to.  I have no idea how this pice goes back into place.  Yikes!

Steve

If you can provide a photo of the piece, maybe we can recognize it ?

Martin

Thanks.  I'll send some photos this evening.

Steve

Martin,

Here is the gizmo, as an attachment.  

Any ideas?

Thanks

Steve

Yes, that's the damper plate.
It is held at the hole, which fits around a cylindrical protruding in the chassis casting and the flat part slides between the
two similar plates on the hinge piece.
The surfaces are treated with kilopoise grease and it's job is to dampen the opening of the large metal lid.

Martin

I just slipped it into position.  Thanks.  Now of course it seems so logical!  So does the torsion bar/spring hook onto the protruding tab on the side of the damper plate?

If this works I'm going to be VERY happy.

Steve