Power Mac G4 General Maintenance

A graphite Power Mac G4 with the side door lowered: three PCI slots and the AGP slot at the top, processor heatsink in the middle, four DIMM slots at the bottom, battery at the top right. Photo: Marco Stadelmaier, Wikimedia Commons, CC BY-SA 3.0

Apple's procedures below cover routine service on the tower Power Mac G4 models in Apple's Power Mac G4/Macintosh Server G4 Service Source: PCI Graphics, AGP Graphics, Gigabit Ethernet, Digital Audio, QuickSilver and QuickSilver 2002, and the Macintosh Server G4 built on them. The Mirrored Drive Doors models have their own manual, cited where they differ. Fault-finding is on Power Mac G4 Troubleshooting.

Before you start

• Shut the machine down and wait for it to cool. Apple's battery sheet says to wait five minutes, and warns that lights glowing on the logic board mean the computer has not been shut down.
• The red LED on the logic board of every model from the AGP Graphics on shows that standby power is present. Do not fit or remove DIMMs or cards while it is lit (p. 211). The supply keeps a standby voltage on the logic board whenever the mains lead is in, so unplug it before working inside (pp. 220–221).
• Ground yourself on the metal PCI access covers at the back before touching anything inside.
• Tools: flat-blade and Phillips screwdrivers, a 2.5 mm Allen key for the power supply, side panels, handles and supports, a jeweller's screwdriver for the I/O panel cover and antenna, needle-nose pliers for the side panels, and an ESD mat (p. 26). See also Recommended Tools.

Opening the case

1. Make sure the security bar is in the unlocked position.
2. Lift the latch on the right side access panel.
3. Lower the panel gently until it lies flat, onto a clean ESD-safe mat or soft cloth so the case is not scratched.

Source: p. 28. To close, raise the panel, lift the latch and press the panel against the case until it snaps into place.

Clock battery

Every 1999–2002 tower uses the same battery, Apple part 922-4028, a 3.6 V lithium cell according to Apple's specification pages (pp. 276–291). Low End Mac describes it as a 3.6 V half-AA. On the PMU-based boards Apple expects it to read 3.3 to 3.7 V; a low battery is replaced before the PMU reset (p. 210).

To replace it:

1. Open the case as above.
2. Note which way round the battery sits; the holder is marked + and −.
3. Pull the battery up out of the holder. A flat-blade screwdriver can spread the two tabs slightly, gently, so they do not break.
4. Fit the new battery with its + and − matching the holder. Apple warns that a battery fitted the wrong way round may explode.
5. Close the case and reset the date and time.

On the Mirrored Drive Doors models, take out a full-length video card first if it covers the battery (pp. 79–80). A leaking lithium-thionyl-chloride cell leaves acidic residue; see Battery Explosion, Capacitor or Corrosion Damage.

PMU reset

The PMU (power management unit) controls power-on, sleep, resets, PRAM and the clock on every model except the PCI Graphics. Apple says many problems are cured by resetting it, and that it should be reset before replacing any module in a machine that will not power up (pp. 208–211):

1. Unplug the mains lead and check the battery reads 3.3 to 3.7 V. If it is low, replace it and wait ten seconds.
2. Press the PMU reset switch (S1) on the logic board once. Do not press it a second time: Apple warns that this can crash the PMU.
3. Wait ten seconds, then reconnect the mains lead and switch on.

Apple warns that touching the logic board circuitry can crash the PMU, and that a crashed PMU cuts battery life "from about five years to about two days" until it is reset. Take the battery out when handling a logic board out of the machine. The reset clears PRAM, so set the date and time afterwards.

The PCI Graphics board uses a Cuda chip in place of the PMU, with a Cuda reset button beside the battery. Apple's full reset for that board is to unplug it, press the front power button, take out the battery for at least ten minutes and refit it the right way round (pp. 213–215).

Memory

DIMMs by model (Apple)

Models	Type	Slots	Sizes
PCI Graphics	PC100 SDRAM, 3.3 V unbuffered, 168-pin	4	8–256 MB; 128 MB modules of 64 or 128 Mbit chips, 256 MB of 128 Mbit
AGP Graphics, Gigabit Ethernet	PC100 SDRAM, 3.3 V unbuffered, 168-pin	4	64–512 MB; 256 MB of 128 or 256 Mbit, 512 MB of 256 Mbit
Digital Audio, QuickSilver, QuickSilver 2002	PC133 SDRAM, 3.3 V unbuffered, 168-pin	3	64–512 MB; same chip rules
Mirrored Drive Doors	PC2100 (133 MHz bus) or PC2700 (167 MHz bus) DDR SDRAM, 2.5 V, 184-pin, unbuffered, no taller than 1.3 in	4	128–512 MB

Sources: pp. 230–231; MDD manual p. 103. Apple says PC-100 DIMMs from late Power Macintosh G3s work in the PCI, AGP and Gigabit Ethernet models but those from older Macs do not, and that Digital Audio machines "must use PC-133 DIMMs". On a 167 MHz Mirrored Drive Doors board, PC2100 memory stops it booting, with a single tone and a flashing front light.

Push down the slot's ejector clips to release a DIMM, hold it by both top corners and lift it straight up. Insert a new one straight down until the ejectors snap shut. Do not rock DIMMs from side to side (pp. 79–80, 268–269).

Processor module

The processor is on a removable module on all these models, and Apple says it "should rarely fail" and is replaced only as a last resort (p. 208). Points from Apple's removal procedures (pp. 47–68):

• The heatsink may be hot. Let the machine cool before starting.
• Release the heatsink clip(s) by pressing down on the top of the clip and lifting its front tab with a small flat-blade screwdriver. On dual-processor QuickSilvers use two screwdrivers, and take care that the one pressing down does not slip onto the logic board.
• Do not bend the processor module when lifting the heatsink off.
• QuickSilvers: the screw at the bottom left of the module "conducts 12 V and could spark if grounded while the computer is on". Make sure the machine is off before removing it. Tighten all four screws snugly on refitting; a loose conducting screw can arc and damage the processor.
• Lift the module straight up by its edges, rocking it gently from side to side, to avoid bending the connector pins.
• Never run the machine without the heatsink: Apple says it "will destroy the processor".
• PCI Graphics: the processor needs the jumper block at J25 for its speed, the right colour, with all its inner metal clips, fitted the right way round. Without it the machine will not boot (pp. 43–46, 212).

Drives

• ATA drives go only in drive bay 3, at the rear, two at most, in a U-shaped carrier. Fit the first drive in the bottom of the carrier and connect the end connector of a dual-drive cable to that bottom drive (pp. 81, 86–87).
• Up to three SCSI drives can be fitted with a SCSI card. Each needs its own SCSI ID; the internal drives are not terminated and the cable has a built-in terminator at its end (pp. 66–68, 253).
• The CD/DVD and Zip carrier on the graphite models can be stiff to push forward because of EMI tape under it (pp. 120–125).
• The QuickSilver 2002ED and Mirrored Drive Doors models use cable select; use Apple's original cables when adding drives (p. 235).

Source: service manual. General hard drive care is on Hard Drive Maintenance and Repair.

Cards

• The graphics card goes in slot 1: a PCI slot on the PCI Graphics model, an AGP slot on the others (p. 232).
• If a card misbehaves, look at its gold edge contacts under a magnifier. Apple suggests a pencil eraser or the contact cleaner Stabilant to remove residue, and warns never to handle cards by the contacts (p. 234).
• Do not use two VGA-to-Macintosh adapters, one at each end of a video cable; Apple says this causes "No video" or black-screen problems (p. 235).

Source: service manual.

Power supply and fans

The supply is replaced as a module. Its part numbers are 661-2256 (PCI Graphics), 661-2256 or 661-2303 (AGP Graphics), 661-2332 (Gigabit Ethernet), 661-2412 (Digital Audio) and 661-2513 or 661-2514 (both QuickSilvers) (pp. 276–291). To remove it:

• Graphite models: open the side panel, remove the CD/DVD bezel and move the drive carrier forward an inch; unplug the power-to-fan connector, drive power cables P6 and P7, the PCI Graphics' P4 to the front panel board, the main cable from the logic board and the hard drive cables; remove the three 2.5 mm Allen screws on the rear vented panel and the screw holding the supply to its shelf; slide it forward and manoeuvre it out past the security bar (pp. 144–149).
• QuickSilvers: remove the CD/DVD/Zip carrier first, then follow the same pattern with four screws holding the supply and its cable (pp. 135–143).
• Move the supply bracket to a replacement, and set its voltage switch to the local mains (115 V in North America) before connecting it (pp. 143, 149).

Source: service manual. The supply's primary side holds mains-derived voltages after unplugging; leave it unplugged for several minutes and treat its capacitors as charged until measured. Testing a supply in the machine is described on Power Mac G4 Troubleshooting#Power supply verification, and community repair notes on Power Mac G4 Troubleshooting#Power supply repair.

All the 1999–2002 towers use the same case fan, 922-3295, in a bracket held by two screws; the QuickSilvers add a processor fan held by two screws and plugged into the logic board (pp. 47–48, 126–134). Apple's chart for intermittent shutdowns asks for clear air vents, a connected and working fan and a properly attached heatsink before anything is replaced (p. 240). Clean dust from the fans and vents with the machine unplugged.

Capacitors

Apple's manuals list no capacitors for these machines, and Console5's Power Macintosh capacitor page has no G4 board. Record the values on the board before replacing anything, and see Capacitor Failure Symptoms.

Related pages

• Power Mac G4
• Power Mac G4 Troubleshooting
• Power Mac G4/Macintosh Server G4 Service Source
• Power Mac G4 Documentation
• Power Mac G4 Cube General Maintenance