Repairing a Hewlett-Packard 7035B X-Y Recorder, Part 1

Before there were pen plotters, in the early 1960s there were X–Y chart recorders, intended to plot one variable, expressed as a voltage, against another. Doing this with speed and precision was a challenge of electromechanical design in the age of discrete transistor circuitry, and some clever tricks we used, such as optical choppers to remove DC offset in amplifiers.