A fault detector apparatus for a printer having a first print head and a second print head with a plurality of print head elements in each print head is disclosed. The apparatus includes a test circuit in signal communication with all the print heads to test the plurality of print head elements. The test circuit includes a test power supply for generating a test voltage, a first resistor, a second resistor, and an analog to digital converter in signal communication with the second resistor. The first resistor is in series connection between the test power supply and the plurality of elements in the first print head. The second resistor in series connection with the test power supply, the first resistor, and the plurality of elements in the second print head. The fault detector apparatus will also work for a printer with only one print head.