Chosen Solution
I replaced the logic board in order to fix a “white screen”. Now there is a healthy chime, but nothing else but black screen.
Using a flashlight hold it against the screen at a sharp angle are you able to see the faint images of your desktop icons? If you do the backlight cables as seen in this IFIXIT guide: iMac Intel 20" EMC 2133 and 2210 Display Panel Replacement in Step10. You may need to check the inverter as well. If you don’t see any icons on the desktop then the GPU logic will need to be checked. I would see if an external monitor shows an image if it does I would inspect the data cable connection to the internal display. If not the GPU board has a problem.
if the screen is black open the mac and disconnect the screen from the logic board then clean the connector and reconnect it. Don’t forget to make sure it’s well connected.
