Aha! That's the problem. Although earlier Tek 400-series (e.g., 453 & 454) had screw access to the tilt handle latch mechanism on the outside of the handle, the newer portables (made since 1976) do not. You have to pull the case off and then you'll likely find a single screw in the center of each handle latch mechanism. Don't lose the parts! And don't stuff that scope into so tight a location that it can't get proper cooling!
Dean