Chosen Solution

Hi, We know there are some test pins on the logic board for diagnose. However, I cannot find the technician guide of 21.5-inch imac late 2012. Could someone tell me where are the test pins and their functions? Or send me the link of the A1418 technician guide Thanks a lot!!!

There are diagnostics LEDs instead. Near to the PSU connector. From bottom upwards -

  1. Indicates that the computer is turned on. This LED will be ON as long as computer is turned on.
  2. Indicates that the computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly.
  3. Indicates that the computer and the GPU are communicating. This LED will be ON when computer is communicating properly with the GPU.
  4. Indicates that the 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 the LCD panel or the cables between LCD and logic board might be installed incorrectly or need replacement.

A. Diagnostic LEDs B. Real-Time Clock (RTC) Reset Pads C. Coin Battery Voltage Test Pads Phew. Hope it helps.