Chosen Solution

When I power up my iMac A1195, all the fans run at top speed and there is no video…black screen. I have tried another lcd screen, same results. It does the same thing even when memory is removed, so I suspect the logic board. Any tips or guides for testing the logic board?

So, I received the replacement logic board today, installed it, and now the iMac starts up as expected. I still have a video problem, but that is because the replacement LCD screen I ordered is bad. At least the old one still works now, multi lines and all. So somehow I must have injured the logic board when I originally installed the replacement LCD screen. I am definitely more careful handling all the parts now. Learned a bit about troubleshooting iMacs, so thanks again for all the communications. Guess I’ll close this post. Thanks. Ron

Ron, just to help you out with the troubleshooting:" Diagnostic LEDs The iMac (17-inch Late 2006) has three built-in diagnostic LEDs and a front power-on/sleep LED on the main logic board that can help you to troubleshoot the computer. To Access the Diagnostic LEDs:v

  1. Follow the take apart instructions to remove the RAM access door, front bezel, and lower EMI shield.
  2. Locate the SO-DIMM slot and LVDS video connector. The three diagnostic LEDs 1, 2, and 3 are located to the left of the battery and under the SATA cable. Note that the LEDs are marked 1, 2, 3 from left to right, as show below. An additional front bezel LED is located in an opening at the center of the right speaker, as shown below

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. 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 LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated. Front LED • Indicates that the computer has power but no video signal (e.g., the computer is starting up or the display has entered Sleep mode, turning off the video signal). This LED will pulse when the entire system has entered Energy Saver mode.

First hook it up to an external monitor to see if it is generating a video signal. Examine the logic board capacitors (cans) for swelling and/or corrosion. Are you getting a normal start up tone? Did you get any beeps when you removed the RAM?