Without further details, most likely the power selector switch. Look for burnt contacts or connections to the switch. Obviously disconnect from the mains before removing covers.
You could try operating the power switch a few, sometimes this can clean dirty contacts.
i cant help much but if you had a pic will help of the unit for other people on here
unplug and have a look inside BE CAREFULL as it prob has capactors in it they will still hold a large charge so dont go poking around what you dont know
if easy to get to the conectors on the board and slide connectors clean them up to a nice bright finsh and reattach taking pics with your phone before takeing any thing apart
if working on low could be selector switches ,dials ?