Beovision MX 7000

28th January 2016

The picture on this set was shifted downwards so that the top of the screen was blank and the bottom of the frame invisible. In addition, trapezium distortion was evident, making scrolling credits look like the introduction to a science fiction film! The geometry adjustments in the service menu all had the correct effect but lacked the range to correct the picture. The +10V and -10V supplies to the frame output chip 4IC4 (TDA8172) were correct, as was the 12V supply to the deflection processor. A replacement for 4IC4 was tried but it made no difference. The chassis was tested in another set to confirm that the scan coils were not defective. The real cause was 4R144 (2M7 in some sets, 2M15 in others) which was open circuit, although it measured normally until it was disconnected. This resistor is pert of a bias network which allows the complete vertical deflection circuit to be DC coupled, therefore making possible a shift function in the service menu. [Beovision MX 7000]