Troubleshooting

Power Mac G4/ Macintosh Server G4

© 2002 Apple Computer, Inc. All rights reserved.

General

Block Diagrams

Power Mac G4 (QuickSilvers/Digital Audio) Block Diagram

Processor Module

Backside

PowerPC G4 microprocessor L2 cache : 256K 1:1

L3 cache

SDRAM DIMM slots

133 MHz Max bus

133 MHz memory bus

PCI slots

Internal CD or DVD connector

Internal Zip drive connector

64-bit 33 MHz PCI bus

EIDE bus

Internal hard drive connectors

Ultra ATA bus

Wireless LAN slot

KeyLargo I/O device and disk controller

UniNorth memory controller and PCI bus bridge

Ethernet PHY

Firewire PHY

66 MHz AGP bus

Boot ROM

AGP 4x slot

Modem slot

Tumbler audio

PMU99 power controller

Internal speaker connector

Ethernet port

Firewire port Firewire port

USB port A USB port B

Headphone jack

Apple speaker mini-jack

Power Mac G4 (Gigabit Ethernet) Block Diagram

Processor Module

Backside

PowerPC G4

L2 cache

microprocessor

Main Logic Board

100 MHz Max bus

100 MHz memory bus

UniNorth memory controller and PCI bus bridge

Ethernet PHY

AGP 2x bus

SDRAM DIMM slots

PCI slots

32-bit 66 MHz PCI bus

AGP 2x slot

PCI-PCI bus bridge

Boot ROM

Internal DVD-ROM connector

Internal Zip drive connector

64-bit 33 MHz PCI bus

Firewire Controller

Firewire PHY

ATA bus

Internal hard drive connectors

Ultra ATA bus

PMU99 power controller

KeyLargo I/O device and disk controller

Modem slot

Screamer sound IC

Wireless LAN slot

Internal speaker connector

Ethernet port

Firewire port Firewire port

USB port A USB port B

Microphone jack Headphone jack

Power Mac G4 (AGP Graphics) Block Diagram

Processor Module

Backside

PowerPC G4

L2 cache

microprocessor

Main Logic Board

100 MHz memory bus

SDRAM DIMM slots

PCI slots

100 MHz Max bus

UniNorth memory controller and PCI bus bridge

AGP 2x bus

AGP 2x slot

32-bit 66 MHz PCI bus

PCI-PCI bus bridge

Internal DVD-ROM connector

Internal Zip drive connector

ATA bus

Internal hard drive connectors

Ultra ATA bus

PMU99 power controller

Boot ROM

Firewire

Firewire

64-bit

controller

PHY

33 MHz

PCI bus

Ethernet

Ethernet

controller

PHY

KeyLargo I/O device and disk controller

Firewire port Firewire port

—Q Ethernet port

Modem slot

Screamer sound IC

Wireless LAN slot

USB port A USB port B

Microphone jack Headphone jack

Internal speaker connector

Power Macintosh G4 (PCI Graphics) Block Diagram

Power Mac Diagram

Power-On Self Test

There is a power-on self test that resides in the ROM of the Power Mac G4. This test automatically runs whenever the computer is powered on after being fully shut down (the power-on self test does not run if the machine is only restarted). If a problem is detected during the test, you will not hear a normal startup chime. Instead, the system will beep as explained below.

Power Mac G4 (all models except PCI Graphics):

  • 1 Beep: No RAM is installed or detected.
  • 2 Beeps: Incompatible RAM types are installed (for example, both SDRAM and EDO installed).
  • 3 Beeps: No RAM banks passed memory testing.
  • 4 Beeps: No good boot images are detected in the boot ROM (and/or there is a bad sys config block).
  • 5 Beeps: The processor is not usable.

Power Macintosh G4 (PCI Graphics):

  • 1 Beep: No RAM is installed or detected.
  • 2 Beeps: Incompatible RAM types are installed (for example, both SDRAM and EDO installed).
  • 3 Beeps: No RAM banks passed memory testing.
  • 4 or 5 Beeps: Bad checksum for the remainder of the boot ROM block. The ROM is bad and probably cannot be fixed.

Logic Board Diagrams

Power Mac G4 (QuickSilvers/Digital Audio) Logic Board Diagram

Ultra ATA Connector

Power

Modem Connector

Front Panel Board

Monitor SDRAM PCI Card DIMM Slots Slot Slots

Ethernet Connector

FireWire Ports (2)

Digital Audio Jack Headphone Jack

Speaker-^fl

Monitor SDRAM PCI Card DIMM Slots Slot Slots

Ethernet Connector

FireWire Ports (2)

Digital Audio Jack Headphone Jack

Ultra ATA Connector

Power

Modem Connector

Front Panel Board

Speaker-^fl

Ds5 Power Mac

Single or Dual Processor

PMU Button Battery

AirPort Connector

IDE Connector

Single or Dual Processor

PMU Button Battery

AirPort Connector

IDE Connector

Power Mac G4 (AGP Graphics/Gigabit Ethernet) Logic Board Diagram

Monitor PCI Slots Card Slot

FireWire Ports (2)

PMU Button Battery

Ultra ATA Connector

Power

Modem Connector Front Panel Board

Speaker—fl

Monitor PCI Slots Card Slot

FireWire Ports (2)

PMU Button Battery

Ultra ATA Connector

Power

Modem Connector Front Panel Board

Speaker—fl

Cuda Button Power Mac

AirPort IDE Processor Connector Connector Plug-In

Slot

SDRAM DIMM Slots

AirPort IDE Processor Connector Connector Plug-In

Slot

Internal

FireWire

Port

(not included on Gigabit models)

SDRAM DIMM Slots

Power Macintosh G4 (PCI Graphics) Logic Board Diagram

Monitor Card Slot PCI Slots

J1 ATA-3

— Ethernet Connector

— Ethernet Connector

Receiving Card Schematics Led Display

Firewire Ports (2) Firewire Card

Modem Connector

SDRAM DIMM Slots

J15 Ultra DMA/33 (ATA Drives) J23 Power-||

Battery/

J8 CD Audi^ J31 Processor J34 J25

Front Panel Plug-In Speaker Jumper Block Board Slot (w/sticker)

Firewire Ports (2) Firewire Card

Modem Connector

SDRAM DIMM Slots

-J2 Firewire Power

Logic Board Troubleshooting

Power Mac G4 (all models except PCI Graphics) Processor Module

The logic board comes with a removable processor module. The processor should rarely fail and should be replaced only as a last resort. Processor modules can be ordered from Service.

Refer to "Processor Module" in the Take Apart chapter for more information.

Resetting the PMU on the Logic Board

The PMU (Power Management Unit) is a microcontroller chip that controls all power functions for the computer. The PMU is a computer within a computer. It has memory, software, firmware,

I/O, two crystals, and a CPU. Its function is to:

  • Tell the computer to turn on, turn off, sleep, wake, idle, etc.
  • Manage system resets from various commands.
  • Maintain parameter RAM (PRAM).
  • Manage the real-time clock.

Important: Be very careful when handling the main logic board. Remove the battery when handling the logic board so the PMU is not affected. The PMU is very sensitive and touching the circuitry on the logic board can cause the PMU to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. The PMU chip is located on the underside of the logic board at U20; refer to the Power Mac G4 (AGP Graphics/ Gigabit Ethernet/Digital Audio) Logic Board Diagrams for the location of the PMU button.

Many system problems can be resolved by resetting the PMU chip. Whenever you have a unit that fails to power up, follow this procedure before replacing any modules:

  1. Disconnect the power cord and check the battery in the battery holder (BT1). The battery should read 3.3 to 3.7 volts. If the battery is bad, replace the battery, wait ten seconds, and then reset the PMU (refer to the next step). If the battery is good, go to the next step.
  2. Press the PMU reset switch (S1) once on the logic board and then proceed to step 3. Do NOT press the PMU reset switch a second time because it could crash the PMU chip.
  3. WAIT ten seconds before connecting the power cord and powering the computer on. If the computer powers on, go to the next step. If the computer does not power on, there is something else wrong with the computer; refer to the symptom/cure chart, "Startup" in this chapter.
  4. Run Apple Hardware Test and return the computer to the customer.

Note: This entire procedure resets the computer's PRAM. Be sure to reset the computer's time, date, and other system parameter settings before returning the computer to the customer.

Logic Board LEDs: Power Mac G4 (all models except PCI Graphics)

There is one red LED on the Power Mac G4 (AGP Graphics/Gigabit Ethernet/Digital Audio/QuickSilver/QuickSilver 2002) logic boards. It indicates that there is power to the board and does not imply a fault condition. Hardware such as DIMMs and PCI cards should not be installed or removed when the LED is on.

Power Macintosh G4 (PCI Graphics)

Processor Module

The logic board comes with a removable processor module. The processor should rarely fail and should be replaced only as a last resort. Processor modules can be ordered from Service.

Note that when you replace the logic board on a Power Macintosh G4 (PCI Graphics), you must also change the processor jumper block and warranty sticker to be compatible with the processor module. Failure to install the jumper block properly will result in a unit that does not boot up. No jumper block is required for Power Mac G4 (AGP Graphics/Gigabit Ethernet/Digital Audio) processors.

Refer to "Processor Module" in the Take Apart chapter for more information.

Resetting the Cuda Chip: Power Macintosh G4 (PCI Graphics)

The Cuda is a microcontroller chip on the Power Macintosh G4 (PCI Graphics) logic board. Its function is to

  • Turn system power on and off.
  • Manage system resets from various commands.
  • Maintain parameter RAM (PRAM).
  • Manage the real-time clock.

Many system problems can be resolved by resetting the Cuda chip (see the Symptom Charts for examples). Press the Cuda reset button on the logic board to reset the Cuda chip. The Cuda reset button is located on the logic board to the right of the battery. Refer to the Logic Board Diagram earlier in this chapter for location information. If you continue to experience system problems, refer to "Resetting the PCI Logic Board" in this chapter.

Resetting the PCI Logic Board

Resetting the logic board can resolve many system problems (see the Symptom/Cure tables for examples). Whenever you have a Power Macintosh G4 (PCI Graphics) computer that fails to power up, you should follow this procedure before replacing any modules.

  1. Unplug the computer.
  2. Press the Power On button on the front of the unit.
  3. Open the side access panel.
  4. Remove the battery from the logic board.
  5. Wait at least 10 minutes before replacing the battery.
  6. Make sure the battery is installed in the correct +/-direction.
  7. Reassemble the computer and test the unit.

Note: This procedure resets the computer's PRAM. Be sure to check the computer's time/date and other system parameter settings afterwards.

Logic Board LEDs: Power Macintosh G4 (PCI Graphics)

There are seven diagnostic LEDs on the Power Mac G4 (PCI Graphics) logic board. A graphic follows showing their location.

DS1 = ATA drive activity

If a CD and/or Zip are attached to the ATA bus, this LED will illuminate at power/on restart time for a few seconds. After that, it is unlikely it will illuminate again in a trouble-free system. If this light stays on for a prolonged period, this is a sign of trouble on the ATA bus. If devices are connected to the ATA bus and this LED is dark at boot time, that is also likely a sign of trouble. If a hard disk drive is attached to this bus, the LED flickers regularly indicating drive activity (reads/writes).

DS4 and DS5 = USB power for downstream devices

(There is no DS2 or DS3 on the board.)

When illuminated, these LEDs indicate that the computer is providing power (+5 V) to downstream USB ports. USB devices do not need to be connected in order for these LEDs to illuminate. However, if one or both of the LEDs is not illuminated and a USB device is/was attached (and the system has completed its boot process), then the logic board has removed downstream power because of a trouble condition.

Since the downstream power is controlled individually for each port, it is possible to have these LEDs in a different state: one off and one on. This way if one port has troubled USB devices, the other port can still be functional. These LEDs are not immediately illuminated at the beginning of a restart or cold power-on. During a successful/normal boot, the sequence will look like:

  1. Unit is powered on and other LEDs will illuminate while DS4 and DS5 are off.
  2. Then DS4 and DS5 on for a second or two
  3. Then off very briefly (1 second)
  4. Then back on (confirms secondary PCI bus is initialized and power now available)

These two LEDs are often useful when troubleshooting an unpredictable system. If they stay on (step 4) then the secondary PCI bus has been initialized which happens relatively late in the boot/hardware initializing process.

DS6 = Ultra ATA bus activity

DS6 indicates Ultra ATA bus activity. DS7 & DS8 = Power Indication

In a working unit, these LEDs should be in sync with each other: both on or both off. If one LED is on and the other is off, there is a problem.

DS9 = CPU Bus Request

When illuminated, this LED indicates that the CPU is requesting the bus. This LED will rarely glow as brightly as the others (like the Ultra ATA LED) given that the CPU is not always requesting the bus, and when it does, the period of time is short. As a result, you may need to watch this LED much more carefully than the others to tell if there is activity. If this LED is ever on continuously and bright, then the system is troubled and likely hung.

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Responses

  • fnan
    Is the Mac g4 cache memory on the logic board?
    7 years ago
  • Veli-Matti Hagman
    Where is the airport slot in a G4 AGP Graphics macintosh?
    7 years ago

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