Methods of and apparatus for detecting pixel element defects in flat panel display (FPDs). Floating pixel elements (FPes) of uncompleted active plates in a manufacturing process are activated with high frequency AC test signals having frequencies higher than frequencies encountered by pixels of completely manufactured FPDs during normal display operation. Application of such high frequency test signals allows detection of pixel defects of pixel elements that exhibit an electrical open circuit at normal display operation frequencies. Because the methods and apparatus allow testing prior to FPD plates being completely manufactured and prior to FPD final assembly, pixel defects can be detected early in the display manufacturing process, thereby resulting in a substantial reduction in production costs.