Chosen Solution

iMac 20" (MB417) I have following symptom on an iMac on power-on:

  • black screen
  • drive briefly spins
  • system powers off within 1-2sec. What is the most likely cause and how can this be tested?

This may take some trial and error to find the problem. Resetting the SMC - First unplug the unit and press the start button for 5 seconds. Next try a PRAM reset, hit the start button and immediately hold down the Option & Command and P and R keys wait till you hear it tone three times. Next re-seat the RAM, here’s how: iMac Intel 20" EMC 2133 and 2210 RAM Replacement This failing you will need to open it and examine the diagnostic LEDs: Here’s a video on how to open it up: http://www.youtube.com/watch?v=8Xs_1QCyP… You will need suction cups: Heavy-Duty Suction Cups (Pair) and a Torx screwdriver set, here’s what I use: [linked product missing or disabled: IF145-022-1] LED Startup Sequence LED #1 = Power available. If no LED is visible: • Verify AC source • Verify known-good AC cable is connected • Verify cable connection between AC inlet and power supply • Verify cable connection between power supply and logic board • Verify power supply LED #1 + LED #2 = Power available, and system is powered on. If second LED is not visible when power button is pressed: • Verify power button connection to logic board • Verify power button functionality • Verify cable connection between power supply and logic board • Verify power supply • Verify logic board LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found. If third LED is not visible after power on: • Verify that MXM video card is seated properly • Verify logic board LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card found, and internal LCD found. If fourth LED is not visible after power on: • Verify cable connections between LCD panel and logic board • Inspect LCD display cables for cable damage • Verify external video functionality, and according to result check the following items: -If external display works then verify/replace LED backlight board -If external display works then verify/replace LCD panel -If external display does not work verify/replace logic board

Update: Do what mayer said first Try booting from your boot dvd (press and hold C to boot from dvd)Did it work?Yes? You probably have a software problem, use your dvd to repair or do a fresh install. If your HDD don’t show up, your HDD is dead.No? You probably have a hardware problem Hardware Your problem could be anything.. I would personally start with ther ram. Depending on how much ram you have you can try to remove one of them and boot from the HDD, if it works the ram you removed is dead. If you have spare ram laying around I would replace both in your machine and try to boot. Try this and let us know what you found.

OK, I went through these steps. Three LEDs lit, external monitor works, but screen completely black. Found a deal on a used screen, swapped it out. Power up the Mac, the screen lit up long enough to show the apple on a grey background then died, now same symptoms as before. Did I just kill another screen? What next, logic board, power supply or inverter? Should the logic board detect the panel even if the inverter and backlight isn’t working? Thanks, Steve L.

omg I need answers to this…I have the imac 20" 2.4Ghz 2008 model…I need to know what is next as steve asked…thank you guys

Alexis: I tried replacing the power supply with no luck. A friend of mine has a G5 iMac with the same symptoms, 3 of 4 diagnostic LEDs lit and for some reason he needed to replace the logic board. So, now I’m deciding between Video Card, Power Supply or the recycling program. Fortunately I do not have an urgent need for this machine. -Steve