Question about Samsung Clp-680dw

Hello, Our Samsung CLP 680 ND printer is acting up. Although our printer is in almost mint condition (well under 10,000 prints), it has recently been throwing out full black copies every time it prints - whether photos or written documents. However, you can see very faintly in the background that the actual print image is present under the black film. We have replaced all 4 toners, but the error remains. Or could this have another cause? No error is shown in the display. We recently installed an Ashampoo Snap 10 programme (Screening) and tried to print a scanned photo on the printer. But only a black sheet appeared. Since then, the printer has actually had this error. Installing the printer driver again did not help either. Maybe there is an expert here who can give us a tip on how to get the device working again. We would be very grateful for that. Kind regards Rainer