Unplug the transformer and undo the screws that secure the rear plate with the terminals on. Drop it down slightly, you may have to jiggle it away from the main case to see inside.
It may help to shine some light inside and then you can operate the transformer to see what is happening to the control arms with the carbon rollers.
It sounds like you may have to remove the case to do any tweaks to adjust it. It isn’t a difficult job.
