I have a big problem, please help me.

[David Negrete]

DOUBT URGENTLY, what should I do if when I move the condenser up it starts to go down by itself? Is this an internal problem? I expect your answer soon because I need urgent help.

[Hobbyst46]

Smear a thin layer of damping grease on the rack of the condenser holder. It will work against free fall and stabilize the condenser's height.
If it does not help, the distance between the moving and static parts of the holder needs tweaking with shims.

[PeteM]

In addition to cleaning and adding a damping grease - and tightening up the clearance on the dovetail slides - some microscopes have an adjustment to tighten up the knob tension.

[EYE C U]

WHAT SCOPE?