The iMac requires trickle voltage (+5 TRKL) in order to poweron. If you are experiencing power problems in the iMac unit, you will want to test for trickle power to pinpoint the location of the problem and to determine whether or not the power supply/analog board is functioning normally. If you have trickle power in the system, the odds are your power/analog board is OK.
In general, you should test for power at the AC outlet first. Next, it is best to check the logic board. In this way, you will be able to immediately pinpoint which module is failing.
The following procedures will explain how to test for power at the AC outlet and at the logic board.
If the unit will not power up from the keyboard, first, unplug the keyboard from the computer. Then, using a known-good power cord, power-on the system using the power button on the front of the computer. If the system powers on, you can assume the AC outlet is good and the problem is with the keyboard. If the system still won't power on, try connecting to a different AC outlet. If the unit powers on this time, you most likely have a problem with the AC outlet. If you still have no power, you may need to reset the PMU chip (power manager) on the logic board (refer to "Resetting the Logic Board" in this chapter).
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