A 3in (2.5cm) point-of-sale printer is a type of thermal printer that uses heat to print receipts on special thermal paper. The printer has a heating element that heats up the paper as it passes through the rollers, creating black marks on the paper where the heat is applied. The heating element and the rollers are two critical components of the thermal printer that can affect the quality of the printout. If the printer is only printing fully black receipts, it means that the heating element is overheating or malfunctioning, causing the entire paper to turn black. The heating element may need to be replaced or repaired by a technician. Alternatively, the rollers may be dirty or damaged, causing the paper to stick to the heating element and get burned. The rollers may need to be cleaned or replaced by a technician.