Actually, there is no "big turbo converter/actuator" or "small turbo converter/actuator".
There is 3 actuators ( round sylinters with a rod coming out of them) that control: the turbine control valve, compressor bypass valve and the wastegate.
The biggest actuator which is located directly under the pressure converters is the turbine control valve actuator. This one is controlled by the first pressure converter from the bulkhead side.
The second actuator, which is located under the bigger turbo, controls the wastegate valve.
The two pressure converters that control these two above, can be adjusted to any position between fully open to fully closed.
Third actuator is located in front of the engine, under the vacuum pump (where the red hose goes to) and this actuator controls the compressor bypass valve. This is an on/off actuator which is controlled by an electric changeover valve that is located right below the first pressure converter from the bulkhead.
The actuator which controls the compressor bypass valve, is opened when revs exeed 3250rpm.
So, the converter that has been changed, controls the turbine control valve. If this control valve stays fully closed, the exhaust gasses have to go thru the small turbine at all times and therefore the big turbines speed is defined by the small turbine (so, lack of power on higher revs). Normally this valve is opened continuously as the engine speed increases so that eventually the small turbine will be bypassed completely.
So usually you have problems either with the first pressure converter or the electric changeover valve. If you had problems with the wastegate actuator/pressure converter then you would have overboost and limp-home-mode
Some say that these actuators can also be "stuck" and limit the normal movement-range off the valve but you can easily check the actuator/valve by moving the rod by hand, if it moves normally it's okay
Just to clarify things (or mix them even more)
