No backlight - LCD working, inverter replaced, backlight replaced

I’ve got an iMac that originally presented with a dead backlight (accompanied by a burning smell from the backlight inverter) a few days after a HDD replacement. Upon inspection it appeared that one of the backlight cables from the inverter to LED was nicked by an LCD screw and may have shorted. With a flashlight to the screen the picture is still present, external display works without issue. 

I started by repairing the cable and replacing the backlight inverter. After that didn’t work I performed a visual inspection of the PSU, Logic board and GPU but could see nothing amiss. I then disassembled the LCD and replaced the LED backlight strip to rule that out. Still no joy!

All diagnostic LED’s are on and I’m getting the correct voltage to the inverter, however the inverter is only outputting around 2V to each LED channel (there are 3 on the 21.5). Have tried PRAM, SMC resets and the diagnostic tools but still no backlight. Any ideas of what else to try before I just use it with an external display permanently?

Cheers!!

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