TFT screen disappears

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Hi all ,

I've designed a tester , the product has got a connector which is supposed to be connected to the tester's connector
The tester has got a 7Inch TFT
Sometimes , whenever I connect the connectors , the TFT screen disappears as if there is no backlight .
I think the problem lies on Ground .
How could I connect 2 Grounds ("Tester Ground & Product Ground" or "Tester Ground & PC Ground") while there is no earth in common ?
I think having a large ground somewhat would solve the problem but isn't there any other way ?

Thanks in advanced

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Need more information.

If the Device Under Test, (DUT), and the Testor are passing digital and analog signals one would usually expect them to share a common ground. They would NOT share a common V+.

There are exceptions to the rule, hence the need for more info on what the two devices are, and the nature of the signals shared between them.

Connecting the two device's grounds does not mean that there needs to be a connection to earth ground.

JC

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Thanks ,

The tester provides power supply for DUT . There is a 19200 b/s communication between the DUT & the tester and no analog data . But the problem persists when there is no communication and there is no power supply for DUT .And the only connection is just the connection of the ground of the tester and the ground of the DUT .
As you know when there is no earth , the potential level of the 2 grounds are different , so connecting these 2 GNDs has consequences . I’ve heard larger ground makes the situation better .

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It makes no sense.

If something is connected together, it is at same potential. Well except that a wire is a small resistance, so currents running through a wire creates a potential difference over the wire. As long as that is kept to some sane levels it is OK.

You have to connect the grounds so they are at the same potential, be that earth or whatever voltage or floating node, otherwise you cannot transfer any data as that requires the ground too.

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during attaching there can be ashort power surge that makes the tft supply drop below its threshold.

perhaps it is an ESD issue.

or a bad reset connection and as such the tft gets a reset (again because of power surge/emc/esd spike)