I have the same problem. Yesterday my F2 burned.
I got my ospi last August, but had no time to try. Yesterday I got my transformer. Firt I tried without the raspi, and the LED worked. Then I connect the raspi V2 and connect the 24V and the F2 start to smoke, so immediatly disconnect the power and remove the raspi. The raspi is not dead, but the F2 look like the picture from the post above.
Then I tried again without the raspi, and the LED still work. I tried the 2nd pin (5V) and the 6th pin (ground) with a multimeter. There I get 36V. This is strange. I don´t like to try again with the raspi. I´m afraid to kill it.
What can I do? 🙁