Troubleshooting Testing for Power - 4
Testing for Power
The iMac requires trickle voltage (+5 TRKL) in order to power-
on. 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.
At the AC Outlet
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 out-
let 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).