T D A 8374 has a black current stabilization loop, that autom atically adjust the black level to the cut-off voltage of the picture tubes three gun cathodes. S ince no current is flow ing w hen the voltage the cathode is equal to the cut-off voltage of the tube, the loop stabilizes at a very sm all gun current. T his �black current� of the three guns is m easured internally and com pared w ith a reference current, to adjust the black level of R G B out. T he black level loop is active during 4 lines at the end of the vertical blanking. In the first line the leakage current is m easured (m ax. acceptable 100
