Chosen Solution
Initially noticed morning after a lightning storm - iMac worked fine prior to this. First 3 diagnostic LED’s are lit, but display back-light doesn’t turn on. There’s also no start up chime sound, but hdd seems to spool up, and white LED is on. No visible signs of damage to power supply, but want to confirm output voltages. Are ps outputs +24v & +12v only?
LED #4 Indicates that the computer and the LCD display panel are communicating. This LED will be • ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement. Contact your insurance agent. I’ve written many insurance reports on lightning hit machines. They usually end up getting replaced with a new machine because the hit can weaken so many things.
I have exact same problem on same machine. I also notice that HD is not spinning at all on startup. Did you manage to get this solved? I do suspect PSU in my case, but I was not able to find any pinout for PSU voltages for this machine.
