How old is it.......
Sometimes one of two conditions exists.
1: Fan dies, there may be a cooling fan which gets old and dies, a new fan makes it work great, fans are generally common computer type.
2: Dust build up.. Not the inverter but two other devices, every couple of years I have to take 'em out pull the cover and hit 'em with the air gun (Wear painters mask when shooting) the dust flys like you would not believe.. Then I replace the cover and take the now much lighter (not all that much) device back in and hook it back up and it works find for a few years.
Home is where I park it!