An operational mode found on many microprocessor-controlled synths, starting in the mid-1980s, which allows certain features and circuits in a synth to be tested. A typical test mode will allow the user to do things such as: test the keyboard for velocity and aftertouch response, test MIDI transmit and receive functions, test performance controls and panel controls, illuminate panel lights and indicators, and (on a polysynth) exercise each voice in isolation.
A test mode might provide for the generation of internal signals as aids in a calibration or repair procedure; for example, specific voltages to tune and scale a VCO. A test mode often provides a means to obtain the version number of the installed operating system, and it might provide a means for loading an operating system update. Another typical feature is to allow the user to read the voltage of the patch memory's backup battery.
On most older synths that have a test mode, the mode is invoked by holding down a button or combination of buttons while turning on the power to the synth. The exact procedure varies widely from one model to the next; it is usually necessary to consult the service manual for the model in question. On newer synths, the test mode is usually accessible from a menu.