Hi,
Thank you for your suggestions advices.
Unfortunately, the contrast settings not helped, the display test was fine in the service menu, I consulted with the service center, he told, later or sooner should be replace the display, therefore:
I bought a brand new Ambit3 Peak HR black again.
The price-value ratio is very good, I have two years warranty.
At last but not least the accuracy is also very good of the built-in positioning system. (GPS)
The following writings perfectly represent it:
https://the5krunner.com/2016/11/05/test-route-for-gps-devices/
Thank you.