Service and Maintenance 8E364xA User’s and Service Guide 223Calibration ReferenceBefore you calibrate the power supply, you must unsecure it by entering thecorrect security code. Refer to “Calibration” on page 82 for more detailedprocedures to unsecure or secure the power supply.Keysight calibration servicesWhen your power supply is due for calibration, contact your local Keysight ServiceCenter for a low-cost calibration. The Keysight E3640A, E3641A, E3642A,E3643A, E3644A, and E3645A power supplies are supported on calibrationprocesses which allow Keysight to provide this service at competitive prices.Calibration intervalRecommended calibration interval for this power supply is 1 year. This will ensurethat your power supply remains within specification for the next calibrationinterval. Keysight does not recommend extending calibration intervals beyond 1year for any application. This criterion for re-adjustment provides the bestlong-term stability.To unsecure the power supply without the security codeTo unsecure the power supply without the correct security code (when you forgetthe security code), follow the steps below. Refer to “Electrostatic Discharge (ESD)Precautions” on page 193 before beginning this procedure.1 Disconnect the power cord and all load connections from the power supply.2 Remove the instrument cover. Refer to the disassembly drawing in “GeneralDisassembly” on page 198.3 Connect the power cord and turn on the calibration mode by holding down theCalibrate key as you turn on the power supply and hold down the key until youhear a long beep. Be careful not to touch the power line connections.4 Apply a short between the two exposed metal pads on JP107 [1] (located nearU121). Refer to “Component locator diagram for the main board assembly —top” on page 233 and “Component locator diagram for the main boardassembly - bottom” on page 234.
