General Information
In this section, we'll discuss some of the fundamental components of a Power Mac G5, with the aim of assessing where and why things most commonly go wrong. Remember, most of the information applies to most Power Mac G5 models, but the exact procedures may vary from model to model.
DDR Memory
In the Power Mac G5, you must install PC3200/400 DDR-SDRAM dual inline memory module (DIMMs) in pairs of equal size and speed. Memory from older Macintosh computers is not compatible. Do not try to install non-DDR memory; it will not fit in the DIMM slots and could cause damage.
The computers ship with a minimum of 256 MB of RAM, provided by a pair of 128 MB DIMMs installed in the two DIMM slots marked “1.” You can add DIMMs, provided they are installed as a pair of equal size, in the two DIMM slots marked “2.” A diagram on the logic board near the DIMM slots illustrates how the pairs must be installed.
Results of Mixing PC2100, PC2700, and PC3200 RAM
The following table describes what happens if you install PC2100, PC2700, or PC3200 memory in either a four-DIMM-slot or an eight-DIMM-slot Power Mac G5 computer.
| When only PC2100 DIMMs are installed: | The computer makes three single tones instead of the startup sound. The LED on the front of the computer fiashes three times, and the computer does not start up. |
| When a mix of PC2100, PC2700, or PC3200 DIMMs is installed: | The computer starts up normally, but neither the computer nor System Profiler recognizes the PC2100 memory. |
| When no memory is installed or memory is not installed correctly: | The computer does not make a normal startup sound. Instead, there is a single tone, and the computer's front LED fiashes about once every 5 seconds. |
PCI and AGP Cards
Power Mac G5 computers have four expansion card slots, three of which accommodate Peripheral Component Interconnect (PCI) cards and one that accepts an Accelerated Graphics Port (AGP) video card. AGP cards and PCI cards have different connectors, so you cannot insert a PCI card into the AGP slot.
NOTE
Maximum power consumption for all four expansion slots (the three PCI expansion cards and the AGP card) should not exceed 90 watts.
AGP Card
The AGP video card, installed in slot 1, contains the graphics processor unit (GPU) and provides the computer's display ports. Slot 1 is designed specifically to accept AGP cards.
NOTE
Certain high-performance AGP graphics cards, when installed in slot 1, block access to the adjacent PCI slot. In this case, PCI cards can be installed in slots 3 and 4 but not in slot 2.
PCI Cards
The remaining three expansion slots, labeled 2, 3, and 4, accommodate PCI cards up to 12 inches long. The PCI slots can accommodate mixed-voltage (+5.0 V, +12 V, or +3.3 V) cards but only at +3.3 V signaling, with 32-bit or 64-bit data widths and a 33 MHz frequency. You can add a 66 MHz card to a 33 MHz PCI slot if the card can operate at the lower 33 MHz rate.
Warning: Installing PCI cards that function only at 66 MHz could damage the computer. However, cards that run at both 66 MHz and 33 MHz may be installed. Check with the card's manufacturer to see if a 66 MHz card also works at 33 MHz.
Resetting the Logic Board
You can resolve many system problems by resetting the logic board. Because the Power Mac G5 (late 2004) uses a System Management Unit (SMU) controller chip rather than a Power Management Unit (PMU) controller chip, the logic board does not include a reset button. Instead, to reset the logic board, do the following:
1. | Shut down the computer. |
2. | Unplug the computer from its power source. |
3. | Wait 15 seconds. |
4. | Plug the power cord back in, and turn on the computer. If the computer does not power on, there is something else wrong with it; refer to the “Startup Failures” section of “Symptom Charts” in this lesson. |
NOTE
The above procedure resets the computer's parameter random-access memory (PRAM). After resetting the logic board, be sure to reset the time, date, and other system parameter settings.
RAM and Processor Verification: POST
A power-on self test (POST) in the Power Mac computer's ROM runs automatically whenever the computer is started up after being fully shut down (the test does not run if the computer is only restarted). If the test detects a problem, the status LED located above the power button on the front of the computer will fiash in the following ways:
One flash: No RAM is installed or detected.
Two flashes: Incompatible RAM types are installed.
Four flashes: No good boot images are detected in the boot ROM (or there is a bad sys config block).
Five flashes: The processor is not usable.
NOTE
The status LED lights up when you press the power button at startup. Do not count this light as one of the diagnostic fiashes.
Front Panel Board Troubleshooting
Certain no-power symptoms may be caused by a failed front panel board or power button. However, troubleshooting these parts by swapping them out with known-good parts can be time consuming. An alternative approach is to build a simple front panel board troubleshooting tool, as shown in the following figure, and then use the procedures described below to test the board and button before actually replacing them.
The tool consists of a known-good front panel board, with a known-good power button and front panel board cable attached.
To use the tool in troubleshooting the front panel board and power button, do the following:
1. | Shut down the computer. |
2. | Disconnect the installed front panel board cable from the logic board. |
3. | Connect the front panel board cable from the troubleshooting tool to the logic board. |
4. | Try to start up the computer by pressing the power button on the trouble shooting tool. Then proceed with the front panel board troubleshooting steps as described in the “Startup Failures” section of “Symptom Charts” in this lesson. |
Power Supply Verification
To power on, the computer's logic board requires a trickle power of +5 V. If the system fails to power on, first reset the SMU. Then perform the following steps to determine whether the problem is related to the power supply.
NOTE
To verify the power supply, you need a multimeter.
