27-01-2016, 11:08 AM
I may be doing a disservice to the Invotron video switch design. The main switching is done using 4051 8:1 analogue mux chips but it appears that the video input buffers each have 4 separate outputs, one for each output of the switcher. So it's possible that when a 4051 doesn't select a given source a transistor is biassed off thereby giving a 2nd break in the signal path. I can probably prove this by making some measurements. The circuits won't be easy to trace as the input buffers are on small sub-modules with SM components.
If this is how it works it's slightly reminiscent of the old Cox video crosspoints. When S3 is off it's simply a pair of emitter followers. When S3 is turned on to block the video, both S1 and S2 are biassed off, thus providing 2 breaks in the signal path. S3 also grounds the signal path.
If this is how it works it's slightly reminiscent of the old Cox video crosspoints. When S3 is off it's simply a pair of emitter followers. When S3 is turned on to block the video, both S1 and S2 are biassed off, thus providing 2 breaks in the signal path. S3 also grounds the signal path.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
