Abstract: A printing apparatus includes a printhead and an ink volume detecting circuit. The printhead contains a plurality of first heating elements for heating ink supplied to the printhead to generate bubbles in the ink and eject the ink through corresponding nozzles. The printhead also contains a second heating element for heating the ink supplied to the printhead, a resistance value of the second heating element being less than the resistance value of each first heating element, and the low resistance value of the second heating element causing the second heating element to burn out and create an open circuit if the volume of the ink is less than a predetermined level. The ink volume detecting circuit is connected to the second heating element for determining if the volume of the ink supplied to the printhead is less than the predetermined level based on a condition of the second heating element.

Abstract: Methods for detecting a short-circuit problem and an open-circuit problem in an ink jet printer. The ink jet printer includes at least an ink jet unit having an input end, a corresponding nozzle, and a control end. The ink jet printer further includes a driving circuit for providing energy to the ink jet unit via the input end. When the ink jet unit receives an ink jet signal via the control end, the ink jet unit can spray ink via the corresponding nozzle according to the energy received via the input end. The short-circuit problem detecting method includes stopping transmitting the ink jet signal to the control end of the ink jet unit, stopping providing energy to the input end of the ink jet unit, and measuring currents flowing through the input end of the inkjet unit.