Chosen Solution
No boot up tones. LEDs 1 2 and 3 are lit and 4 is dark. Display is dark. Some say it is the logic board and some say it is the power supply. Is there a way to narrow it down?
Hook it up to an external display to narrow down your diagnostic. If it’s what I think it is you should be able to shine a flashlight at an angle to the screen and see the desktop. To see if you can get a tone again, reset the SMC How to reset the SMC Choose Apple menu > Shut Down.After your Mac shuts down, press Shift-Control-Option on the left side of the built-in keyboard, then press the power button at the same time. …Release all keys.Press the power button again to turn on your Mac.UPDATEI would bet on it being the inverter:iMac Intel 20" EMC 2133 and 2210 Inverter Replacement
