The JLG Curtis Instruments 17400700 is a joystick controller used on aerial lift platforms to provide operator input for platform movement and safety functions such as emergency stop. Common failures reported for this model include power supply dropout or degraded signal due to worn contacts, burned-out output transistors in the drive circuitry, and loss of function keys caused by internal fuse blowouts or capacitor leakage. Initial checks should verify that the controller receives its rated input voltage (typically 24 V DC), inspect all connectors for corrosion or loose pins, and confirm that the status LEDs and error codes are within normal operating ranges before proceeding to board-level diagnostics.[oss-gpt-20b]