Has anyone any experience with error code 804?

I started to weld aluminum, and the aluminum rod other end touched the metal table while I was welding and the TIG stopped working. Now It shows 804 in the display.

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I measured the inverter and it doesn't work correctly. But it is very difficult to find the fault without schematics. Also the build "quality" is far from good. Many components are added afterwards on top of the other and so on.
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