Unscrew the inverter board (the one with a heat sink) in order to access the IGBTs.

There are two IGBTs (Insulated Gate Bipolar Transistor) on this board that are likely to fail. These electronic components switch high voltages, and large currents, at a rapid rate, so they are subject to wear and tear. The IGBTs are bolted to a hefty heat sink.

This picture shows the inverter board with heat sink.

There are 3 components attached to the heatsink: a bridge cell on the left, an IGBT GT60N321 in the middle and another type of IGBT (GT30J322) on the right (not visible in the photo).