Pixelated Readout Hameg 404-2

Hello,
I purchased a Hameg 404-2. It works normally as an analog scope. But what doesn't work is the readout, the display of the numbers and letters on the screen. These are pixelated. I have restored several vintage scopes (Hameg, Tektronix, Leader) but have no experience with this type of scope. Where can I suspect the error, which module is in question? What is the procedure? There is a circuit diagram, but it doesn't really help me. I checked the supply voltages and everything was spot on. Can someone help me? Thank you.