Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. http://electronicshelponline.blogspot.com/ In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.
Ensure your testing procedure is perfect. If your testing procedure is proven, then you will need to send it for repair. At that point, either your scale or grid assembly is damaged or requires adjusting.
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Precision Tool Works - www.precisiontoolworks.com