Power Macintosh G3 (Blue and White) Troubleshooting
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Fault-finding on the Power Macintosh G3 (Blue and White). Apple's symptom charts list cures in order of likelihood: try the first, test, and refit the original part before moving to the next cure.[1] The same charts cover the Macintosh Server G3 (Blue and White).
Before you start
[edit | edit source]- At least one PC-100 SDRAM DIMM must be fitted; the board has no soldered memory.[1]
- Check the J25 jumper block: black 300 MHz, blue 350 MHz, white 400 MHz, yellow 450 MHz, with its metal clips inside and its bump towards the top of the board opposite pin 1. Several of Apple's no-start charts include this check.[1]
- The computer starts without the graphics card in slot 1 but does not work properly.[1]
Resets
[edit | edit source]- Cuda reset: press S4, to the right of the battery on the logic board.[1]
- Logic board reset, which Apple says to do before replacing any module on a unit that will not power up: unplug the computer, press the power button on the front, open the side panel, remove the battery, wait at least 10 minutes, refit the battery the right way round, then reassemble and test. Set the date, time and other settings again afterwards.[1]
- PRAM: hold Command-Option-P-R during startup.[1] A 68kMLA member with several of these machines reports that they are sensitive to scrambled PRAM after a low battery or repeated incomplete startups, and that removing the battery and the mains and leaving them overnight (at least 12 hours) brings them back.[2]
Power-on self test
[edit | edit source]The ROM runs a self test after a full shutdown (not on a restart). If it finds a fault there is no startup chime; the computer beeps instead.[1]
| Beeps | Meaning | Apple's cures |
|---|---|---|
| 1 | No RAM installed or detected | Reseat the SDRAM; if none is fitted, fit a known-good PC-100 DIMM in the top slot; replace DIMMs one at a time with known-good ones, starting with the top slot; reseat, then replace, the processor module; replace the logic board[1] |
| 2 | Incompatible RAM types (for example EDO with SDRAM) | Fit only PC-100 SDRAM; replace DIMMs one at a time; reseat, then replace, the processor module; replace the logic board[1] |
| 3 | No RAM bank passed the memory test | Replace DIMMs one at a time with known-good PC-100 DIMMs; reseat, then replace, the processor module; replace the logic board[1] |
| 4 or 5 | Bad checksum in the boot ROM | Replace the logic board[1] |
Logic board LEDs
[edit | edit source]Seven LEDs on the logic board help with a machine that starts but misbehaves.[1]
| LED | Function | What to look for |
|---|---|---|
| DS1 | ATA bus activity (CD-ROM and Zip bus) | Lights for a few seconds at startup if devices are fitted. On for a long time, or dark at startup with devices fitted, points to trouble on that bus |
| DS4, DS5 | USB power to port 2 (upper) and port 1 (lower) | In a normal start they stay off, come on for a second or two, go off for about a second and come on again, which shows the secondary PCI bus is up. One off after startup with a USB device attached means the board has cut power to that port |
| DS6 | Ultra ATA bus activity | Flickers with hard disk activity |
| DS7, DS8 | Power indication | Must both be on or both off. One on and one off means a fault |
| DS9 | Processor bus request | Faint and flickering in normal use. On continuously and bright means the system has hung |
There is no DS2 or DS3.[1]
Power supply verification
[edit | edit source]The logic board needs the +5 V trickle supply to start. Leave the 20-pin cable plugged into the logic board, plug in a known-good power cord and measure each pin against pin 16 (ground).[1]
| Condition | Pin | Expected | If missing |
|---|---|---|---|
| Computer off, cord plugged in | 9 | About +5 V (trickle) | Recheck the meter, then replace the power supply |
| Running | 1 | About +3.3 V | Replace the power supply |
| Running | 4 | About +5 V | Replace the power supply |
| Running | 10 | About +12 V | Replace the power supply |
Between the trickle check and the running checks, press the front power button with the power cable firmly plugged into the front panel board. If the computer starts, the supply is good. If the supply fan does not spin, check that the black and yellow fan cable from the supply is plugged into the black and red fan connector. Apple's connector drawing also shows pin 8 as power good, pin 14 as power on, pin 12 as -12 V and pins 2, 11 as +3.3 V.[1]
System
[edit | edit source]| Symptom | Apple's cures, in order |
|---|---|
| Completely dead | Check that DS7 and DS8 are in step; check the outlet and power cord; check the voltage switch; run the power supply verification; disconnect the keyboard and start the computer from the front of the case (if it starts, replace the USB keyboard); reset the Cuda chip, then the logic board; replace the logic board[1] |
| Supply fan running, but no chime, black screen, no drive access and no front LED | Check the voltage switch; check J25 for colour and direction; reseat the processor module with its lever down; reseat the DIMMs; reset the logic board; replace the logic board, processor module[1] |
| Fan running, LED on, drive accessed, but no chime and a black screen | Reseat the DIMMs; check J25; check the monitor and sound cables are in the right ports[1] |
| Powers up, fan and drive spinning, LED lit, no video | Reseat and test the DIMMs one at a time; check J25; reseat the processor; check internal SCSI cabling and that all cards are seated; remove all cards except the graphics card and disconnect the hard drives; replace the graphics card, logic board, processor[1] |
| Shuts down intermittently | Check the fan cable and fan; clear the vents and keep the side panel shut; check and replace the power cord; check the battery; reset the Cuda chip and logic board; replace the power supply, logic board, processor module[1] |
| Crashes, hangs or freezes | Mac OS 8.5.1 with Mac OS ROM 1.2; clean install from the computer's own CD; extensions off; Disk First Aid; MacTest Pro in loop mode overnight; clear PRAM; test the DIMMs one at a time; disconnect all USB devices and add them back one at a time; reset the logic board; replace the logic board, processor module[1] |
| Clicking, chirping, thumping or rubbing | Remove the PCI cards and refit them one at a time; reseat the CD-ROM and Zip carrier and cables; remove the hard drive; replace the power supply, processor module, logic board, I/O card[1] |
| Small pieces of metal loose in the case | Remove them; take out and inspect the logic board, cards, power supply and drive carrier; run MacTest Pro[1] |
A 68kMLA member's loose Rev. 1 board, with no case or battery, would not start from its power button although it passed MacTest Pro once running. The members who looked at it suspected the power-on, reset or Cuda circuit, or damage while the board was out of its case.[2]
Video and sound
[edit | edit source]| Symptom | Apple's cures, in order |
|---|---|
| Black screen, but chime, drive activity, fan and LED | Check the video cable, card and any VGA adapter; reseat and test the DIMMs (PC-100 only); check J25 and its clips; clear PRAM; reset the Cuda chip and logic board; replace the monitor cable; try a known-good monitor; replace the graphics card, processor module, logic board[1] |
| Black screen, no chime, no drive activity, but fan and LED on | Check the video connections; check J25; reset the Cuda chip and logic board; reseat the graphics card, DIMMs and processor module; test the DIMMs; replace the monitor cable, graphics card, processor module, logic board, power supply[1] |
| Chime and the screen lights, but nothing is displayed | Check the video connections; reset the Cuda chip and logic board; reseat all PCI cards, the SDRAM and the processor module; replace the monitor cable; try a known-good monitor; replace the processor module, logic board[1] |
| Screen jitter | Reseat, then replace, the graphics card[1] |
| No sound from the speaker | Boot from CD and with extensions off; disconnect microphones and speakers; check the volume and mute; clear PRAM; check the speaker cable on J34; try headphones (if the jack works, replace the speaker; if not, the logic board)[1] |
The graphics card belongs in slot 1, the 32-bit 66 MHz 3.3 V slot.[1]
Hard drives
[edit | edit source]- A single internal hard drive does not spin: check it in Drive Setup and reinstall its driver; check the cables; replace the data cable; try another power lead (P5, P2 or P3); replace the drive, then the power supply.[1]
- Flashing question mark: boot from the system CD to see whether the drive appears; check the system software; run Disk First Aid and update the driver with Drive Setup 1.6.2; disconnect external SCSI devices; reinstall the system; replace the data cable, then the drive.[1]
- Data corruption on a Rev. 1 board: the built-in Ultra ATA controller does not handle UDMA reliably with many later drives. Limit the drive to multiword DMA mode 2, move it to a PCI ATA or SCSI card, or use a Rev. 2 board (CMD chip marked 646US-402 at U1).[3][4]
- Before treating an HFS Plus drive as faulty, find out whether Norton Utilities 3.5.1 or earlier has been run on it.[1]
- See Hard Drive Maintenance and Repair.
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32 Apple Computer, Power Macintosh G3/Macintosh Server G3 (Blue and White) Service Source, hosted here as File:Power Macintosh G3 and Macintosh Server G3 (Blue and White) Service Source.pdf (see Power Macintosh G3 (Blue and White) Service Source). PDF page numbers: power-on self test p. 199; Cuda reset p. 200; Resetting the Logic Board and battery pp. 201-202; Logic Board LEDs pp. 203-207; Processor and Jumper Block pp. 208-210; PCI slots and card cleaning pp. 211-213; SDRAM pp. 214-216; Power Supply Verification pp. 217-221; HFS Plus pp. 222-224; VGA adapters p. 225; Symptom Charts: System pp. 227-235, Error Beeps pp. 236-237, Video and Sound pp. 238-244, Hard Drive pp. 245-246, Miscellaneous p. 262.
- ↑ 2.0 2.1 68kMLA forum thread "The B&W G3 that won't die... or live.", November-December 2022. SiliconValleyPirate: B&Ws are sensitive to scrambled PRAM from a low battery or repeated stop-start and incomplete startups; the cure is to pull the PRAM battery and mains and leave them overnight (12 hours minimum); a board that will not start from its power button points to the PMU, Cuda, reset or power-on circuit. Big Ben: ran a loose board on an ATX supply, then noted the ATX power-good signal is +5 V where the G3 board uses 3.3 V; after a day unplugged the board started more easily. Community experience.
- ↑ Wikipedia, "Power Macintosh G3" (retrieved 2026-10-02). Revision 1 ATA/33 controller problems: two hard drives cannot be connected and newer drives give data errors; workarounds are replacement boards, SCSI, Ultra ATA or SATA PCI cards, or limiting the drive to multiword DMA mode 2; Mac OS X disables UDMA on affected boards. History only.
- ↑ Low End Mac, "Blue & White Power Mac G3" (retrieved 2026-10-02). Rev. 1 CMD chip PCI646U2, Rev. 2 646US-402, at U1; Rev. 1 does not support UDMA properly or master/slave pairs; Mac OS X disables UDMA on the Rev. 1 board. Secondary source.