I have a Shark SV780 n. It would not turn on. I pulled it apart to replace? the switch. Turns out it was not the switch itself but the MOSFET that actually supplies power to the motor. I replaced the CEB83A3G on the power/charging board and, bingo! Works great. The transistor is available on line but I had to buy 10.

It is a surface mount device. I tried a heat gun to remove it but other components started to come off. With good soldering iron simply heat the entire transistor with the iron and slide it off the board. Apply a small amount of solder on the exposed pads and place the new one on the board. Heat the entire device with your soldering iron and flow the solder. Needless to say, don't keep the transistor hot for long periods but it is designed to take the heat of soldering.

it was not easy but doable.