There is a 2 amp fuse right after the power connector in the live line. Check it and if blown replace once. If it blows right away there are other problems.
I suspect your problem most likely is the
starter board.
Power transformer failures are rare and if that is the problem then the unit is not worth the cost of repair likely. To test it you will have to disconnect everything and check all windings for continuity, starting on the primary side.
I suspect the board you need is AWX7087 , if you can find one. The whole parts issue with these types of products is a disgrace, with flouting of the law left right and center. If your unit is actually only six years from manufacture then parts should be available. The law requires 7. But I bet they are not available as Pioneer did not hand over to Onkyo in an ethical manner. Anyhow Pioneer parts service is your only hope.
By the way the location of that unit sounds totally inappropriate. Heat kills and has probably killed yours.