Repair of a Mastech MS7221 Volt/mA Voltage Current Calibrator (Source/Output Step DC 0-10V 0-24mA Tester Meter).
I purchased the MS7221 off Ebay as condition unknown/possibly faulty. I took a chance and bought it as these units are very useful for simulating 0-10vdc & 4-20mA signals. No instrument tech should be without one.
Far from complete but shows the basics of the on/off button and psu front end.