Power Macintosh G3 All-in-One Troubleshooting
.jpg)
Fault-finding on the Power Macintosh G3 All-in-One. 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 Service Source has no power supply test for this model. Faults in the display and power supply boards, which owners report most often, are covered at the end from community repair reports. Before working in the upper case, read CRT Discharge Procedure.
Before you start
[edit | edit source]- The computer starts from the power key on the ADB keyboard, so test with a working keyboard connected.[2]
- Check J16 (processor: red 233 MHz, white 266 MHz) and J28 (power supply). Apple says a missing or wrong J28 setting stops the computer starting.[1]
- At least one SDRAM DIMM must be fitted. Several machines thought dead have started once known-good memory was fitted.[2][3]
- The logic board needs both the ROM DIMM and the processor module to run, and starts without the I/O card but does not work properly.[1]
Resets
[edit | edit source]- Cuda reset: press the Cuda reset button on the logic board, beside the PCI slots.[1]
- Logic board reset, which Apple says to do before replacing any module on a unit that will not power up: unplug the computer, remove the battery, unplug the power supply cable from the logic board and press the Power On button, wait at least 10 minutes, refit the battery the right way round, reassemble and test.[1]
- PRAM: Command-Option-P-R during startup, before "Welcome to Macintosh".[1] A 68kMLA member reports that the battery-out reset clears a scrambled PRAM on the All-in-One when the keyboard reset does not.[4]
System
[edit | edit source]| Symptom | Apple's cures, in order |
|---|---|
| No apparent power: fan not running, no LED | Check the power cord at both ends; check the internal power cables; reseat the ROM DIMM and processor module; reset the Cuda chip; reset the logic board; check J28 and J16; replace the power cord, voltage regulator, power supply, logic board, processor module[1] |
| Fan running, but no chime, black screen, no drive access and no front LED | Check J28; check J16; reseat the processor module with its lever down; reseat the ROM DIMM; replace the voltage regulator, logic board, processor module[1] |
| Fan running, LED on, drive accessed, but no chime and a black screen | Check J28; reseat the ROM DIMM[1] |
| Clicking, chirping, thumping or rubbing | Remove the PCI cards and refit them one at a time; remove the hard drive; replace the power supply, processor module, logic board, floppy cable, floppy drive, I/O card[1] |
| Shuts down intermittently | Clear the air vents (thermal protection may shut it down; it should recover in 30-40 minutes); 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 or hangs | Mac OS 8.1 with its enabler; clean install; extensions off; clear PRAM; test the DIMMs one at a time; replace the logic board, processor module[1] |
Error chords
[edit | edit source]- One-part error chord at startup: disconnect the IDE cable from the hard drive and restart (if normal, initialise the drive and retest; replace it if the chord returns); disconnect the floppy cable and restart (if normal, replace the floppy drive); reseat the processor module; replace the logic board, then the processor module.[1]
- Eight-part chord (death chimes): replace the DIMMs one at a time with known-good ones; replace the logic board.[1]
Video
[edit | edit source]The built-in display gets its signal from the I/O card through the RGB cable, and its power from the power supply board through cables P908 and P913. The symptom charts below pair P905 with P913, but the take-apart chapter describes P905 as the two-wire fan cable.[1]
| Symptom | Apple's cures, in order |
|---|---|
| Black screen, but chime, drive activity, fan and LED | Brightness; clear PRAM; reset the Cuda chip and logic board; check the cables on the analog and CRT video boards; check that P505 on the analog board connects to P913 and P905 on the power supply and P507 to P908; replace the RGB cable; test the DIMMs; replace the logic board, processor module[1] |
| Black screen, no chime, no drive activity, but fan and LED on | Reset the Cuda chip and logic board; test the DIMMs; check the analog and CRT video board cables and P505, P507 as above; replace the RGB cable, logic board, power supply, processor module[1] |
| Chime and the screen lights, but nothing is displayed | Reset the Cuda chip and logic board; check the analog and CRT video board cables and P505, P507; replace the RGB cable, logic board, processor module[1] |
To separate the computer from the display, connect an external monitor to the monitor port. Owners have done this by pulling the personality card or disconnecting the internal video connections; a working logic board then drives the external monitor.[5][6]
Drives, sound and peripherals
[edit | edit source]- Single hard drive does not spin: replace the drive power cable, then the drive, then the power supply. Original IDE drives are now often dead.[1][3]
- No internal SCSI drives (the optional Zip): check SCSI IDs and termination; replace the SCSI cable, power supply, logic board, processor module.[1]
- Floppy drive faults: known-good disk, cable, drive, logic board, processor module. If a disk will not eject, hold the mouse button down while switching on.[1]
- No sound from the speakers: disconnect microphones and external speakers; check volume and mute; clear PRAM and check the speaker connection; try headphones (if the jack works, replace the speaker or logic board); replace the I/O audio card, speaker, logic board.[1]
- Cursor does not move or keyboard dead: check and clean the mouse, plug it into the computer's ADB port, check the keyboard cable; replace the ADB cable, mouse or keyboard, logic board.[1]
- PCI card faults: clean the card's gold fingers with a pencil eraser.[1]
Display and power supply faults (owners' reports)
[edit | edit source]The power supply board feeds both the logic board and the analog board, and a fault on the display side can stop the whole machine.[6] Owners' findings:
| Symptom | Finding | Source |
|---|---|---|
| Picture distorts with zapping; arcing; machine cuts off when the display powers up | Failing LG flyback transformer (6174Z-1009A or -1009D). Replacements are sold; one owner's CRT came back after reflowing the flyback's solder joints | [6][5] |
| No chime or LED, fan on, relay clicks and the supply hisses; analog board buzzes and cuts out | Display-side fault loading the supply. Disconnect the analog board or internal video and test the logic board on an external monitor. One owner replaced the flyback, the C5404 output transistor, every capacitor and the CRT without curing it | [6][2] |
| Starts after the personality card's display connection is unplugged, trips with it connected | Fault on the display side; one owner found it this way | [7] |
| Main rails rise partway and collapse with a buzz and a fan twitch; standby 5 V present | Power supply board fault (the machine chimed when run from an ATX supply) | [7] |
| Intermittent power faults | Cracked joints on the 20-pin connector on the power supply board; reflow it | [6] |
| Machine chirps and restarts, supply clicks | One owner recapped all four of his machines for this; he notes it could also be the voltage regulator | [2] |
Capacitor values for the analog board and CRT video board are on Power Macintosh G3 All-in-One Capacitor Replacement Guide.
Related pages
[edit | edit source]- Power Macintosh G3 All-in-One General Maintenance
- Power Macintosh G3 (Beige) Troubleshooting (same logic board; includes Apple's power supply test for the desktop and minitower)
- CRT Discharge Procedure
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 Apple Computer, Power Macintosh G3 All-In-One Service Source, hosted here as File:Power Macintosh G3 All-In-One Service Source.pdf (see Power Macintosh G3 All-In-One Service Source). PDF page numbers: Cuda chip p. 7; Resetting the Logic Board pp. 8-9; logic board diagram p. 24; Troubleshooting: general p. 122; voltage regulator p. 123; processor module p. 124; J16 p. 125; J28 p. 126; I/O cards p. 127; card connector cleaning p. 128; Symptom Charts: System pp. 129-134, Error Chords p. 135, Video pp. 136-138, Floppy Drive pp. 139-140, Hard Drive pp. 141-142, Peripherals pp. 143-145, CD-ROM Drive p. 146, Miscellaneous p. 147; power supply cable descriptions p. 78; analog board connections p. 83.
- ↑ 2.0 2.1 2.2 2.3 68kMLA forum thread "Power Macintosh G3 All In One (Molar Mac) Power Supply, Analog Board, And Deflection Board Recap List", November 2023 to November 2024. jajan547: the AIO needs ADB soft power (keyboard power key) to start; with the LED on, a black screen and the fan running but no chime, add RAM; his machines chirped and restarted constantly with the supply clicking (possibly the voltage regulator); some had battery damage. wottle: no fan or LED on one machine although its logic board worked in a desktop; two others needed only RAM and then ran with crackling from the analog board and flyback. Phipli: the jumper inverts the soft-power logic, so changing it makes the board power on as soon as power is applied, handy for minimal testing; ATX supplies can be used for testing. Durosity: replaced the flyback and the C5404 transistor and recapped most of the power and analogue boards; R726 on the analogue board ran very hot. Community repair report.
- ↑ 3.0 3.1 68kMLA forum thread "G3 AIO Molar Macs wont start", September 2021. NickNick: two AIOs with LED and fans running but no picture; new RAM brought one back with the CRT crackling; the other needed a replacement logic board and processor, and its old board had corroded resistors around a crystal near the processor; beachycove: a chime means the POST has passed; reseat the logic board tray and everything on the board; original IDE drives nearly always fail. Community repair report.
- ↑ 68kMLA forum thread "No video after PRAM battery replaced (Beige G3 Tower)", January 2015. Macdrone: unplug, remove the battery, press the power button, refit the battery and boot from CD; works on the AIO, tower and desktop whatever the ROM. Community experience.
- ↑ 5.0 5.1 68kMLA forum thread "Molar Mac - Dead Display", September 2026. sciencegirl100: with the personality card pulled the AIO boots with an external monitor; the internal CRT showed no static at power-on; flyback 6174Z-1009D; a mark on the upper case possibly from arcing; reflowing the flyback's solder joints brought the CRT back, though it sometimes cuts out. Community repair report.
- ↑ 6.0 6.1 6.2 6.3 6.4 68kMLA forum thread "G3 AIO 'Molar' issues - Flyback? Caps?", August-September 2024. Durosity: with the internal video connections in place, no chime and no LED, fan on, the supply clicked a relay and hissed, the analog board buzzed and cut out and some parts got very hot; with them disconnected the logic board worked on an external monitor; with the analog board disconnected the system boots, and the supply's analog board outputs read correctly unloaded but drop under load; replacing the flyback, all capacitors and the CRT did not cure his machine. Daniël: LG flybacks in the AIO and tray-loading iMac overheat, cook their winding lacquer and arc, distorting the image and, when bad, shutting the machine off as soon as the flyback is powered. Torbar: reflow the 20-pin connector on the power supply board, whose joints tend to crack. LightBulbFun: check heavy boards for cracks after shipping. croissantking: use a meter in continuity mode to look for shorted diodes and ceramic capacitors. Community repair report.
- ↑ 7.0 7.1 68kMLA forum thread "PowerMac G3 AIO PSU Recapping Help", August-September 2026. cgober: standby 5 V steady at about 4.9 V; at power-on the 5 V, 3.3 V and 12 V rails rise partway then collapse together with a fan twitch and a buzz; the machine chimed on an ATX supply; with everything disconnected the supply still clicked and its rails fell away. Durosity: his faulty AIO starts with the personality card ribbon detached and trips with it connected; the analog or neck board may also be at fault. Community repair report.