Specifications

iMac (21.5-inch, Late 2012) iMac (27-inch, Late 2012)
Important
Only use side-to-side motion when wiping or polishing display panel.
Do not use the sticky silicone roller to clean the display panel.
Diagnostic LEDs
Both the iMac (21.5-inch, Late 2012) and iMac (27-inch, Late 2012) have four built-in diagnostic light-emitting diodes (LEDs) and two test pads on
the logic board that can help you to troubleshoot the computer.
WARNING
Be extremely careful when troubleshooting or working inside the computer when it is plugged into an electrical outlet.
DO NOT touch the logic board or power supply while the computer is plugged in.
Be careful not to short the volt meter test leads to other components or to physically damage delicate components on the logic
board when positioning probes.
A = Troubleshooting LEDs
B = Coin cell voltage test pads (measure the coin backup battery, expected voltage is 3 VDC)
C = Reset for real time clock, RTC (short pads to reset the RTC)