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ground loop with HDMI & VGA both connecte

Question asked by HankZ on Feb 26, 2014
Latest reply on Feb 28, 2014 by lopihyilfrtuky4e

Here is the situation; We are using the ADV7513 HDMI driver chip and the ADV7125 VGA driver chip. 

If we connect both outputs to the same monitor the HDMI image has a "speckle" pattern, particularly in areas of high or low brightness (please see images attached)

When we disconnect the VGA cable the problem goes away. 

As this appears to be a ground loop issue I attempted to isolate the VGA ground with a small resistor and was able to go as low as 3.9 ohms and found that the problem would be corrected, I do not want to place low ohm resistors in the ground of the VGA.

 

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