Chosen Solution
I’m trying to diagnose a backlight problem related to an iMac logic board. Symptoms/Notes: Boots fine but screen is blackImage can be seen when shining a torch on screenExternal monitor works fineAll 4 diagnostic leds are lit Other things: LED invertor board is goodPower supply goodLCD and cables all goodCable when plugged into LVDS connector has continuity through all 30 pins So the problem definitely seems to be with the logic board but I’m not sure where, or how to test further. I don’t know the history of the board but it does appear to possibly have had the cables janked upon opening at some point as the LCD temp sensor is ripped off. The only thing I can think of is to replace the LVDS connector but upon close inspection all joints look good, all pins have continuity through a cable, and the correct pins are grounded. Is there anything else I can test? any other known logic board components, fuses etc. related the backlight? I’ve been trying to find some schematics but had no luck.
Shane Murphy I am sure that you already checked your diagnostic LED’s but just forgot to mention it. LED #1 • Indicates that the trickle voltage from the power supply has been detected by the main 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 the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty. LED #2 • Indicates that the main logic board has detected proper power from the power supply when the computer is turned on and that logic board voltage regulators are functioning properly. This LED will be ON when the computer is turned on and the power supply is working correctly. LED #3 • Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement. LED #4 • Indicates that the computer and the LCD 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 display, then the LCD panel, the LED backlight board, or the cables between might be installed incorrectly or need replacement. I’d check the backlight board first. Again this is a generic answer since you did not specify what model your iMac is.
any news?I got the exact same problem!
