Same as mine.
They are in fact quite simple. In the middle of the window, on the opening edge, opposite where the handle goes in to the window (the handles are normally retained by two woodscrews through the escutcheon plate. Release these two screws and the handle comes out. You will then see that it is just like a door handle; square section mild steel bar.
If you then look on the edge of the window moulding (the bit that is lost to view when closed) you will see one or two metal plates, recessed into the moulding.
Removing this/these should provide access to the internal workings.
All they in fact are, are one or two bell cranks (i.e. small levers sitting at circa 90 degrees to the two rods, that are inserted into the window, top and bottom).
Next remove the cover plates (if any) top and bottom of the window and diagnose the problem.
It will usually be with the bell crank/s.
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