I also have a SL-B3. this has the same slotted hinge for the cover tab, but sits in a slot. The Q2 hinge is screwed to the rear plinth. Funny it will hold up the B3 lid, but not the Q2 lid. They don't seem to be much different in weight.I have the same deck, but I'm not home right now. I'm not sure if the hinges are adjustable. Maybe others will know.
Before I got dzkfraser's recommend, I took a pair of pliers and gave a squeeze on the sides of the hinge just above the pin (not on the plastic upper part that holds the cover tabs) on both sides. For now it's holding the cover up. It must have gave it just enough friction to hold it up. If it starts dropping again I will try his method.Gary, did that work? (the instructions in the link that @dzkfraser provided)?

Unless springs are VERY worn out, this method should work. I have successfully used it in my dad's SL-D3.I had the same problem with my Q2 - I fixed it using the instructions at this link: