Even you did not post picture, I guess you have your CRT display blink?

try to adjust Synchronize Potentiometer--open the CRT back case cover (shut off power for safety), even you can see that Potentiometer from the top of your CRT cover from the grill holes , but I suggest you open the back caver. locate the position then power on,  use insulated screwdriver turning slowly CW or CCW , this one fix by wax after adjusting waxing it again

If you cannot find where ? send the picture from the top of CRT --I will point to you

Good Luck and please feed back here

Vigilant

I have a sinumerik 850m as well, the display comes up for a while and starts blinking, how to make the display start working again? We also replaced the battery recently

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Split from Error in boot of Sinumerik 850M.