Chosen Solution

My in-laws gave me their iMac that got taken out when lighting hit the cable TV lines in their yard. Two cable boxes and the connected TVs are dead. The cable modem was dead. And the iMac that was connected directly to the cable modem doesn’t work. I don’t think any lighting energy traveled through the AC power lines into the house, just through the cable lines. So I’m working on the theory that the logic board absorbed a lot of energy from the modem. Interestingly, this computer was repaired under AppleCare a couple of years ago - the logic board was replaced because the Ethernet port was not working. The computer won’t start up. Nothing appears on the screen. The power button will start the fans and I can feel air coming from the top vent. I can power off the computer by holding the power button in. The computer is mine to keep. They’ve already replaced it with a new one. I’ve got plenty of computers and I’m not going to run a life-supporting medical device on this thing. But I feel the call, the challenge, to bring this thing back to life. A logic board is a given. Other parts and components that may need repair or replacement: CPUPower supplyDisplay components, inverter, etc.LCD displayHard driveBluetooth adapterWiFi adapterOptical drive So, what do you all think about how deep I may get into this before it works again?

Get a pile of cash about equal to twice the original cost of the machine. Understand the concept of “cascading failure”: https://en.wikipedia.org/wiki/Cascading_… Quit when the stack runs out. In my opinion, the whole thing is worth what you can sell the stand for.

rstrobel, I’d start with the routing checks as suggested by Apple. You just never know. Resetting the System Management Controller (SMC) The System Management Controller (SMC) is a chip on logic board that controls all power functions. If computer is experiencing any power issue, such as not starting up, not displaying video, sleep issues, or fan noise issues, resetting SMC may resolve it. To reset SMC on an iMac:

  1. From Apple menu, choose Shut Down (or if the computer is not responding, hold power button for approximately ten seconds until it powers off).
  2. Unplug all cables from computer, including power cord.
  3. Press and hold the power button for 5 seconds.
  4. Release the power button.
  5. Attach the computer’s power cable, making sure power button is not being pressed. Note: If you press the power button while inserting the power cord, the iMac will enter a mode in which the fans run at full speed.
  6. Press the power button to turn on the computer. Resetting Parameter RAM (PRAM) PRAM stores certain system and device settings in a location that Mac OS X can access quickly. Exactly which settings are stored in the computer’s PRAM varies depending on the type of computer as well as the types of devices and drives connected. To reset PRAM:
  7. Shut down the computer.
  8. Locate the following keys on keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in Step 4. Note: If the keyboard does not have an Option key, use the Alt key instead.
  9. Press power button.
  10. Immediately press and hold Command-Option-P-R keys. Important: You must press this key combination before the gray screen appears.
  11. Hold down keys until the computer restarts, and you hear the startup chime a second time.
  12. Release keys. No Power, Dead Unit Unlikely cause: speakers Quick Check Symptoms Quick Check No Power, Dead Unit • No power • No fan spin • No startup chime • No image on external display • No hard drive or optical drive activity
  13. Verify power source.
  14. Verify power cable.
  15. Listen closely for signs of activity from system including: rotating fans, hard drive or optical drive activity, startup chime, etc. Deep Dive
  16. Power ON system. Verify if there is any indication that the system has powered up (fan rotation, hard drive or optical drive noise, backlight turns on). Yes The symptom is powering up. Go to Won’t Start Up symptom flow. No Go to step 2.
  17. Locate diagnostic LEDs in bottom case vents. Plug AC cord into system. Verify if diagnostic LED #1 turns ON. You may alternately check for presence of a 12V DC signal between pin 4 and pin 1 of logic board. Yes Standby power voltage being supplied by power supply. Go to step 3. No Replace power supply.
  18. Press power button while monitoring diagnostic LEDs. Verify if LED #2 turns ON and remain ON after pressing the power button. You may alternately check for a power request signal between pin 12 and pin 1 of logic board. Yes Power supply functioning and logic board detects supply voltages. Go to Won’t Start Up symptom flow. No Go to step 4.
  19. Disconnect AC cable then remove power supply and carefully inspect connectors between AC inlet and power supply, then DC connectors and cables between power supply and logic board, for damage or poor connections. Yes Replace damaged part. No Go to step 5.
  20. Inspect power button and verify if it is properly connected to the logic board. Yes Go to step 6. No Reconnect power button.
  21. Disconnect power button from logic board. Inspect cable and connector for damage. Verify continuity between the two pins of power button when it is pressed. Yes Power button is functioning correctly. Reconnect power button to logic board and go to step 7. No Power button faulty. Replace rear housing (which includes power button).
  22. Press power button and Verify if system turns ON. You may alternately check for presence of a 12V DC signal between pin 11 and pin 1 of logic board when power button is pressed. Yes Power supply functioning. If system still won’t boot, go to Won’t Start Up symptom flow. No Replace DC power cable. Go to step 8.
  23. Press power button and verify if system turns ON. Yes Issue solved with replaced DC power cable. No Replace power supply. Go to step 9.
  24. Press power button and verify if system turns ON. Yes Issue solved with replaced power supply. No Reinstall power supply and replace logic board. Diagnostic LEDs Depending on iMac model, there are either three or four built-in diagnostic LEDs on the logic board that can help troubleshoot the computer. LEDs are located on bottom right edge of logic board (under a piece of black mylar tape) and can only be seen when looking through lower vents of rear housing. LED Functions LED #1 • Indicates that trickle voltage from power supply has been detected by logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when computer has been shut down or put to sleep. The LED will turn off only if AC power source is disconnected or power supply is faulty. LED #2 • Indicates that logic board has detected power from power supply when computer is turned on. This LED will be ON when computer is turned on and power supply and voltage regulators are working correctly. LED #3 • Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then video card might be installed incorrectly or need replacement. Note: LED #3 is not present on models with integrated graphics. LED #4 • Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED 4 is ON and there is no image on display, then LCD panel, LED backlight board, or cables between might be installed incorrectly or need replacement. 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 Logic Board Test Point Function Pin 1 Ground Pin 4 Standby 12V power (permanent power coming from power supply and present as long as AC cable is connected, even if computer is off); corresponds to LED #1 Pin 6 Backlight Control pulse width modulated signal (from logic board to LED backlight board, to adjust the backlight level setting according to user setup) Pin 11 12V Run-Mode power to logic board (coming from power supply, present as long as system is on or asleep); corresponds to LED #2 Pin 12 Power On Request signal (from logic board to power supply when power button is pressed) Pin 13 Backlight Enable (signal from logic board to Backlight Controller board, to enable backlight Resetting the System Management Controller (SMC) The System Management Controller (SMC) is a chip on logic board that controls all power functions. If computer is experiencing any power issue, such as not starting up, not displaying video, sleep issues, or fan noise issues, resetting SMC may resolve it. To reset SMC on an iMac:
  25. From Apple menu, choose Shut Down (or if the computer is not responding, hold power button for approximately ten seconds until it powers off).
  26. Unplug all cables from computer, including power cord.
  27. Press and hold the power button for 5 seconds.
  28. Release the power button.
  29. Attach the computer’s power cable, making sure power button is not being pressed. Note: If you press the power button while inserting the power cord, the iMac will enter a mode in which the fans run at full speed. For more information, refer to: kBase #TS1433: iMac: Fans run at full speed after computer turns on
  30. Press the power button to turn on the computer. Resetting Parameter RAM (PRAM) PRAM stores certain system and device settings in a location that Mac OS X can access quickly. Exactly which settings are stored in the computer’s PRAM varies depending on the type of computer as well as the types of devices and drives connected. To reset PRAM:
  31. Shut down the computer.
  32. Locate the following keys on keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in Step 4. Note: If the keyboard does not have an Option key, use the Alt key instead.
  33. Press power button.
  34. Immediately press and hold Command-Option-P-R keys. Important: You must press this key combination before the gray screen appears.
  35. Hold down keys until the computer restarts, and you hear the startup chime a second time.
  36. Release keys.

Hey rstrobel, I’d recommend that you get it repaired or if you have insurance even better. Check if your home insurance can do something about that. For now if you want to repair it yourself, start with replacing the power supply of your iMac -Let me know how it goes.

The fact you are getting a reaction when you press the power button makes me think the logic board is more likely gone here Vs the power supply. It’s possible a single leg got blown but for now I would recommend you try out a known good logic board. Sadly, lightning tends to damage more than one part so its possible other parts are damaged more so with externally connected devices like a FireWire HD or USB keyboard or mouse.

I would reset the battery, as a matter of fact reset all removal components, memory, hard drive, etc. If that doesn’t work…toast it….