short circuit on logic board, only two diagnostic lights now

i've got this late 2015 21.5" 4K iMac on my bench. I had it open and was doing some work, and my son knocked my SPI programmer and a bunch of test leads onto the powered up logic board.

there was a brief crackle and a little wisp of smoke.

i had the iMac powered on, with three of the four diag lights on. i expected the fourth off as i had the LCD panel removed. now i'm only getting two green lights, and no display either with the LCD panel back on or via external monitor.

i have attempted SMC reset.

where can i start?