If the rest of the machine is playing fine I would suspect a component on the LCD matrix display has died. It’s quite common for some of the Maygay ones to burn out, but generally the Bellfruit/Mazooma ones are pretty reliable but I wouldn’t rule it out, especially considering the age of the machine. Take a close look at the matrix unit to see if there’s any burnt out components. You should be able to get a fairly cheap second hand one I would have thought. Make sure you make a note of the matrix display model number as they do vary between machines from the same manufacturer.