General Information
Power Button Pads on Logic Board
With the top case removed, the power button is disconnected. Instead of having to reconnect the top case to turn on the system, there are two pads on the logic board that can be shorted across (with a tool like a metal fiathead screwdriver) to act as the power button.
These pads are located near the edge of the logic board, just above center of the hard drive. It is marked “POWER BUTTON.” The pads are separated with a vertical white line.
Resetting the PMU
You will recall from Lesson 3, “General Troubleshooting Theory,” resetting the Power Management Unit (PMU) is a quick fix. The PMU reset sequence for the PowerBook G4 is different than for other Macintosh models. Use the following procedure or the PMU reset pad (see “PMU Reset Pads on Logic Board”).
1. | If the computer is on, turn it off. |
2. | Disconnect the power adapter and remove the main battery. |
3. | |
4. | Install the main battery and connect the power adapter. |
5. | Press the power button to restart the computer. |
NOTE
Warning: Resetting the PMU will permanently remove a RAM disk, if present, and all of its contents. You will also need to reset the settings in Date & Time preferences.
PMU Reset Pads on Logic Board
In addition to the power button pads on the logic board, there are pads for PMU reset, which work when their pads are shorted together (with a tool like a metal fiathead screwdriver). The pads are separated with a white horizontal line between the pads. The pads are located near the edge of the logic board, just above center of the hard drive.
NOTE
Warning: Resetting the PMU will permanently remove a RAM disk, if present, and all of its contents. You will also need to reset the settings in Date & Time preferences.
Caps Lock LED Power Check (Partial)
There are situations when the system is giving indications that it is shut down (no sleep light, no hard drive access, screen is dark, no blower, and so on). However, the logic board may still be running. In this case, the logic board is drawing power and generating heat.
NOTE
Warning: In this situation, if the computer is put in an enclosed environment like a carrying bag, the computer can overheat.
Check this situation by pressing the Caps Lock key. If the LED glows, the PMU is running on the logic board. If pressing Caps Lock fails to wake the computer, try closing and opening the lid. If that fails, hold the power button down for 6 seconds to force a shut down of the computer. Restart the system to check if it boots up normally.
NOTE
In earlier PowerBook models the keyboard was connected directly to the PMU, and this method worked under all conditions. However, since the keyboard is now a USB device, if the Mac OS is hung, the keyboard cannot respond. So if the Caps Lock light does not come on, the computer may be drawing power. If in doubt, hold the power button down for 6 seconds to force a shut down of the computer.