A digital-to-analog converter (DAC)/amplifier testing system for use in an electron-beam (e-beam) mask writer, the e-beam mask writer including a plurality of DAC/amplifier circuits to output analog voltage signals, each DAC/amplifier circuit having a first output terminal and a second output terminal, the first output terminals of the plurality of DAC/amplifier circuits being respectively coupled to deflection plates of the e-beam mask writer to provide the output analog voltages as deflection voltages, is provided. The testing system including a summation circuit to sum voltage signals and to output a summation signal indicating the sum of the received analog voltage signals and an analyzer circuit to digitize the summation signal and to detect to compare the digitized summation signal with an error tolerance range to detect whether at least one of the DAC/amplifier circuits is experiencing an operating error.