I have been attempting to fault find on an old IMO Jaguar Cub inverter which runs a lather in my workshop, I have found a transistor which is not behaving as it should (dead short on any 2 terminals), my experience is limited to switching out parts which directly replace but this circuit is from the 80's and the transistor is obsolete. Can anyone point me either to a replacement or what to look for in one? I would prefer not to get it wrong and screw something else up!

I believe this is the datasheet for what i have and the image of the transistor is attached..

http://www.irf.com/product-info/datasheets/data/irgbc20f.pdf

 

I searched with similar basic parameters like to220 package and 600 volts. There were many candidates that could work, but IRG4BC20FPbF seems to be a modern replacement for your IGBT,

https://www.infineon.com/cms/en/pro...?productType=5546d462533600a401533d3fd0a24edc

Test conditions seems to be the same including 50 ohm gate resistor.