Chosen Solution
This is what my display shows:
I’ve replaced the LCD, LVDS cable, LCD temp sensor. I’ve also try plugging in an external monitor and it shows perfectly no signs of the faint image. When I boot the system display it randomly shows a normal image sometimes but when it does, the system powers off or goes to sleep. I can hit the space bar to wake it up sometimes but once I restart the system, it goes back to the fainted screen. Could it be the GPU still even though the external monitors shows perfect? Or the logic board? Power supply?
My bet would be a failing inverter or cable. There is no guide for replacing it the 24” but the on for the 20” should work just fine: The Cable Inverter , power is Apple part #922-8856 There is a possibility the 24” does not have an inverter, you’ll have to look. In that case replace the inverter cable iMac Intel 20" EMC 2133 and 2210 Inverter Replacement Here the complete Apple Service Source on your machine: http://tim.id.au/laptops/apple/imac/imac…
I think you’re facing two issues which are interrelated. First I would replace the PRAM battery which is located on the bottom right side of the logic board. Follow this guide to Step 12 iMac Intel 24" EMC 2134 and 2211 Hard Drive Replacement
Once replaced lets reset the display Start by choosing Apple menu > System Preferences …Select the Displays Preference PaneClick the Color tab
As soon as you do the washed out screen should be gone.
