Power Mac G4 Troubleshooting

Power Mac G4 (QuickSilver) with the side door lowered. Photo: baku13, Wikimedia Commons, CC BY-SA 3.0

Fault-finding for the tower Power Mac G4 models, from Apple's Power Mac G4/Macintosh Server G4 Service Source (PCI Graphics to QuickSilver 2002) and the separate Mirrored Drive Doors manual, with community repair reports where Apple's manuals stop at "replace the power supply". Apple lists cures in order of likelihood: try the first, check whether the symptom persists, and refit the original module before trying the next (p. 236). Opening the case, the battery, the PMU reset and module removal are on Power Mac G4 General Maintenance.

Before you start

• Check the voltage switch on the back of the power supply is set for the local mains. Apple's chart for a completely dead machine includes it (p. 237).
• Check the clock battery reads 3.3 to 3.7 V, and reset the PMU (or, on the PCI Graphics, the Cuda) before replacing anything (pp. 209–215).
• Work out which model you have; several cures differ by model. See Power Mac G4#Telling the models apart.

Source: service manual.

Power-on self test

The boot ROM runs a self test after a full shutdown (not after a restart). If it finds a fault there is no start-up chime; the machine beeps instead (pp. 203–204, 243–245).

Start-up beeps

Beeps	Meaning	Apple's cures, in order
1	No RAM installed or detected	If no DIMM is fitted, put a known-good one in the top slot; reseat the DIMMs; run Apple Hardware Test and replace bad DIMMs one at a time; reseat the processor module; replace the processor module; replace the logic board
2	Incompatible RAM types fitted	Check only SDRAM DIMMs are fitted (PC-100 in PCI/AGP/Gigabit Ethernet, PC-133 in Digital Audio and QuickSilvers); run Apple Hardware Test and replace bad DIMMs; reseat the processor module; replace the processor module; replace the logic board
3	No RAM bank passed the memory test	Run Apple Hardware Test and replace bad DIMMs; reseat the processor module; replace the processor module; replace the logic board
4	No good boot image in the boot ROM, or a bad system configuration block (PCI Graphics: bad boot ROM checksum)	Replace the processor module; replace the logic board. Apple says the ROM "is probably bad and cannot be fixed"
5	Processor not usable (PCI Graphics: bad boot ROM checksum)	Replace the processor module; replace the logic board

The Mirrored Drive Doors models use the same beep codes; on them, two beeps mean memory other than DDR266 SDRAM is fitted (p. 113).

Power supply verification

To start, the logic board needs a standby "trickle" voltage from the supply, present whenever the mains lead is in. Apple's test for a machine with "no apparent power" (pp. 220–229):

1. Open the case to reach the supply connector on the logic board. Leave the connector plugged in and probe from the back.
2. Plug in a known-good mains lead. Do not switch on.
3. Measure the trickle voltage as given in the table. If it is missing, check the probes and measure again; if it is still missing, replace the supply.
4. Press the front power button. If the machine starts normally, the supply is good.
5. If it does not, check that the supply fan spins. If it does not, replace the supply.
6. With the black lead on the ground pin given in the table, measure about +3.3 V at pin 1, +5 V at pin 4 and +12 V at pin 10. If any is missing, replace the supply. If all are present, the supply is not the cause.

Trickle voltage and ground pin by model

Models	Connector	Trickle voltage (red lead)	Ground (black lead)	Notes
PCI Graphics, AGP Graphics	20-pin	About +5 V at pin 9	Pin 16	Pin 8 is power OK; pin 14 is power on; pin 12 is −12 V
Gigabit Ethernet, Digital Audio	22-pin	About +28 V at pin 22	Pin 11	Pin 15 is power on; pin 13 is −12 V; pin 9 not connected
QuickSilver, QuickSilver 2002	22-pin plus 4-pin P4	About +25 V at pin 22	Pin 11	Pin 9 also carries +25 V; P4 (two +12 V, two common) feeds the processor module

Source: pp. 220–229. Apple's figures are approximate and the manual gives no tolerances.

The Mirrored Drive Doors models use a 24-pin connector. Apple's text says the board needs a +5 V trickle (pin 1, purple), but its procedure measures about +12 V from pin 12 to pin 24 with the machine plugged in and off, then +3.3 V at pin 6, +5 V at pin 3 and +12 V at pin 10 with it running; pin 14 (white) is a +25 V standby line. The full pinout is on Power Mac G4 (Mirrored Drive Doors) Service Source (pp. 107–108).

Logic board LEDs

On the AGP Graphics and later boards there is one red LED, which shows standby power and does not mean a fault (p. 211). The PCI Graphics board has seven diagnostic LEDs (pp. 215–219):

PCI Graphics logic board LEDs

LED	Meaning
DS1	ATA activity. Lights for a few seconds at start-up if a CD or Zip is on the bus; on for a long time, or dark at boot with devices attached, points to an ATA bus problem
DS4, DS5	+5 V to the upper and lower USB ports. In a normal boot they come on, go off for about a second, then stay on once the secondary PCI bus is set up. A dark LED after boot with a USB device attached means the board has cut power to that port because of a fault
DS6	Ultra ATA activity
DS7, DS8	Power. Both should be on or both off; one on and one off is a fault
DS9	Processor bus request. Normally a faint flicker; on steadily and brightly means the system is probably hung

Start-up

Start-up symptoms

Symptom	Apple's cures, in order
Completely dead: no fan, power button not lit	Check the outlet; replace the mains lead; check the supply's voltage switch; check the trickle voltage and replace the supply if it fails; disconnect external devices including the monitor; remove internal cards; disconnect the internal hard drives; check the modem connector J27 for bent pins (replace the logic board if any); replace the logic board
Fan and drive spin, power light on, but no chime or video	Reset the logic board (PMU, or PCI board reset); PCI Graphics: check the J25 jumper block; reseat the processor module; check all PCI and AGP cards are seated; replace the processor module; replace the logic board
Power light and machine stay on only while the power button is held	QuickSilvers: reseat the processor module; replace the processor module; replace the logic board; replace the power supply. Digital Audio: replace the power supply; reseat the processor module; replace the logic board; replace the processor module
Shuts down intermittently	Check the mains lead and supply; check the air vents are clear; check the fan is connected and running; check the heatsink is attached; PCI Graphics: reset the Cuda; reset the logic board; replace the power supply; replace the logic board
Shuts down almost immediately after start-up	PCI Graphics: reset the Cuda; reset the logic board; check J27 for bent pins; replace the processor module; replace the power supply; replace the logic board
Memory error message	Reseat the DIMMs; check only SDRAM of the right speed is fitted; run Apple Hardware Test and replace bad DIMMs one at a time
Flashing question mark	Start from the restore CD; if the drive appears, run Disk Utility or Disk First Aid, update the driver and reinstall the system software; otherwise reseat the drive's data and power cables, then replace the drive
Quits or hangs intermittently	Software checks (application, PRAM, clean install, extensions, Disk Utility); run Apple Hardware Test in loop mode (Control-L) to test memory; reset the logic board; replace the processor module; replace the logic board

Source: pp. 237–242. On the Mirrored Drive Doors models Apple adds that several bus-powered FireWire devices with an Apple ADC 17-inch CRT display can overload the supply and shut the system down: use powered FireWire devices or reduce the display's draw (p. 112).

Video

Video

Symptom	Apple's cures, in order
Black screen, but chime, drive, fan and power light all present	Check the video cable, card connections and pins; try a known-good monitor; remove third-party devices; reseat the video card; PCI Graphics: check the J25 jumper block; clear PRAM; PCI Graphics: reset the Cuda; reset the logic board; replace the video card; replace the logic board
Black screen, no chime, drive does not run, but fan running and power light on	PCI Graphics: check J25; check video cable and pins; PCI Graphics: reset the Cuda; reset the logic board; reseat the video card; reseat the processor module; replace the processor module; replace the logic board
Chime, screen lights, but stays grey	Reset the Cuda (PCI Graphics) or logic board; reseat all PCI cards, DIMMs and the processor module; replace the processor module; replace the logic board
Distorted video	Update the video card driver and firmware; adjust the monitor; try a known-good monitor; reseat the cable and card; check any VGA adapters (never one at each end of the cable); replace the video card
Screen jitter	Look for environmental causes; check cables; update driver and firmware; try a known-good monitor; reseat, then replace, the video card; replace the logic board

Source: pp. 235, 246–250.

Sound, drives and ports

Sound, drives, USB, FireWire and network

Symptom	Apple's cures, in order
No sound from the internal speaker	Disconnect microphones and external speakers; check volume and mute; start with third-party extensions off (Mac OS 9); clear PRAM; check the speaker cable on the logic board; plug in headphones: if they work, replace the speaker, if not, the logic board
No sound from Apple Pro Speakers (Digital Audio, QuickSilvers)	Push the plug fully into the Apple speaker port past both detents, with a slight twist; check volume and balance; clear PRAM; reinstall system software; replace the speakers
Single ATA drive does not spin; flashing question mark	Check the cables; try another connector on the supply's harness (a bad harness means a new supply); replace the drive
Internal SCSI drives missing	Check Apple System Profiler; update drivers; check for duplicate IDs; check termination (internal drives unterminated, terminator at the cable end); reseat the SCSI card and cable; remove devices one at a time; replace the cable; replace the card; try another power connector
CD/DVD tray will not open	Reseat the drive's data and power cables; check the bezel is seated; reseat the data cable on the logic board; try a known-good disc; replace the drive
CD/DVD icon missing	Check Apple System Profiler; try a known-good disc; eject a stuck disc by holding the mouse button at restart; turn off third-party extensions; update the drive firmware; reinstall software; reseat cables; try another harness connector; replace the drive; replace the logic board only if other devices on the bus fail too
Zip drive missing or ejects disks	Check it shows as ID 1 (slave) with no jumper on the 6-pin connector; reseat cables; replace the drive or cable
Mouse or keyboard dead	Check connections; try the mouse on a port on the computer instead of the keyboard (replace the keyboard if that works); swap USB ports (a dead port means a new logic board); replace the mouse or keyboard
FireWire device missing	Check power, cable and Apple System Profiler; check drivers; look for bent or dirty pins; try the other port (a dead port means a new logic board); replace the cable, device, then logic board
No network	Try a known-good cable; select Ethernet in AppleTalk or TCP/IP; clear PRAM; test from the restore CD; try a known-good hub port; replace the logic board

Source: pp. 251–261. Apple's modem charts (pp. 262–266) deal with drivers, scripts and phone lines; the hardware cures are to reseat and then replace the modem card and its cable.

Power supply repair

Apple's manuals treat the supply as a module and stop at "replace the power supply". The Mirrored Drive Doors manual warns that its supply should not be opened (p. 46). Owners who do repair them report:

• On a Mirrored Drive Doors supply (Samsung LQ3352ABPoWB, Apple 614-0224), an iFixit Answers contributor advised checking the fuse first and named the most common failures on these supplies as a shorted mains capacitor, a shorted bridge rectifier and shorted power MOSFETs. Another contributor in the same thread, with two 933 MHz QuickSilvers used for audio work, reported supply faults on both and called the supply the most common G4 fault.
• An owner of a dual 867 MHz Mirrored Drive Doors machine described the power button glowing and the fan running for about two seconds, then stopping. One reply reported the same symptom on another MDD cured by a new supply; another suggested replacing the 3.6 V battery and resetting the PMU first. Apple's own order for the Digital Audio puts the supply first for this symptom and for the QuickSilvers last (p. 242).

Before opening a supply, unplug it and leave it for several minutes. The primary-side capacitors charge to about 340 V on 240 V mains (240 × √2) and can hold it; measure across them before touching the board. If the fuse has blown, follow the iFixit contributor's list and test the bridge rectifier, the switching MOSFETs and the mains capacitor for shorts before fitting a new fuse. See Capacitor Failure Symptoms.

Related pages

• Power Mac G4
• Power Mac G4 General Maintenance
• Power Mac G4/Macintosh Server G4 Service Source
• Power Mac G4 (Mirrored Drive Doors) Service Source
• Power Mac G4 Cube Troubleshooting