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I have designed a board that is acting weird when you touch the touch screen, turn on and off relays, and even if you touch any wire specify ground(on jacket of wire). I want to know how can I determine this is due to ground loop or not.
Below image show how power supply shift up (or ground) and down wile touch the screen.

enter image description here

you can see even better on my amplifier output which is only transimpedance amplifier with gain 1M.

enter image description here

This is only two layer board with ground plan on both top and bottom, as you can see on below image.

Please let me know if you need more information.

Shahreza
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  • No way to do this with such a big board and no schematic. Looks like you'll have to debug it yourself, step by step. –  Dec 16 '20 at 17:41
  • @Brian Thanks for reply, my question where should I start. I do not want make another layout until I know the issue – Shahreza Dec 16 '20 at 17:42
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    You should start in the middle of your signal processing chain. Break the linkage and see if it still happens. If it doesn't then the problem happens earlier in the chain. Either way, you've done one thing and one test and halved the number of areas that the problem might be in. Use your brain and imagination. – Andy aka Dec 16 '20 at 17:44

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