Power Macintosh G3 (Beige) General Maintenance

A beige minitower with its side panel off (Museo8bits, Wikimedia Commons, CC BY-SA 2.5)

Routine work on the desktop and minitower Power Macintosh G3 (Beige): opening the desktop case, the PRAM battery, memory, the processor module and its jumper, the voltage regulator card, the power supply and the drives. The steps follow Apple's Service Source, which is written for the desktop case. The Power Macintosh G3 All-in-One uses the same logic board in a different case; see Power Macintosh G3 All-in-One General Maintenance for that machine.

Before you start

• Unplug the computer and wear an earthed wrist strap while handling the boards.
• Check the voltage switch on the back of the power supply before plugging in: 115 for 100-130 V, 230 for 200-270 V. Apple warns that a wrong setting can damage the computer.
• Have a known-good SDRAM DIMM to hand. The board has no soldered memory and will not start without a DIMM.
• Tools: Phillips screwdrivers, a small flat-blade screwdriver for the heat sink clip, and a multimeter for the power supply checks on Power Macintosh G3 (Beige) Troubleshooting. See Recommended Tools.

Opening the desktop case

1. Press the two tabs at the front corners of the top housing, pull the housing forward 1-2 in and lift it straight up. It covers the top, front and both sides.
2. Open the card retainer baffle: lift it with one hand while pushing in the tab that holds it to the internal chassis.
3. Release the chassis latches, flip out the support foot, and swing up the internal chassis, which carries the power supply and drives. Lock it up with the support arm, its tab in the hole in the bottom chassis. Apple's warning is never to work with the chassis up unless the arm is down and secure.
4. The logic board lies in the bottom of the case, with the hard drive in front of it.

Close the case in the reverse order: lift the support arm out of its hole, lower the chassis, close the expansion card cover, push the release switches outwards and fold the support foot back in.

PRAM battery

The battery sits near the front left corner of the logic board as you face the computer. Open the case, prise up one side of the battery cover with a screwdriver and lift the battery out. Apple specifies a 3.6 V lithium battery; Low End Mac gives the size as half-AA. Fit the new cell the right way round; Apple's logic board reset procedure reminds you to check the +/- direction.

Take an old battery out of a machine going into storage. Leaking cells damage the board around them; see Battery Explosion, Capacitor or Corrosion Damage. 68kMLA members report that these machines often need more than a Command-Option-P-R reset after a battery change: unplug the computer, take the battery out, press the power button, refit the battery and start up.

Memory

Memory for the beige G3

Item	Requirement
Main memory	168-pin, 64-bit, 3.3 V unbuffered SDRAM DIMMs in three slots; any size in any slot; no performance gain from pairs
Speed	70 ns or faster (Service Source); 100 MHz/10 ns (Apple specification pages)
Maximum	384 MB (Service Source); 192 MB desktop and 384 MB minitower (Apple specification pages)
Height in the desktop	Low-profile DIMMs, 1.15 in maximum
256 MB DIMMs	Built with 128 Mb chips (16 chips); DIMMs with 256 Mb chips are seen at half size
Video memory	2 MB SGRAM on the board; one 144-pin 3.3 V SGRAM SO-DIMM slot for up to 6 MB in all. Never fit the 256K or 512K video DIMMs from older Macs

To fit a DIMM, open the case, push down the ejectors on the slot, line up the notches with the ribs in the slot and press the module in. The SGRAM SO-DIMM sits flat and parallel to the board; spread the arms of its slot to release it.

Processor module and jumper

The processor module sits in a ZIF socket. To remove it:

1. Take out the screw that holds the processor module wire to the logic board. When refitting, use a hand screwdriver: there is a capacitor next to the screw hole.
2. Press down on the heat sink clip, lift its front tab with a small flat-blade screwdriver, and take off the clip and heat sink. The heat sink may be hot.
3. Lift the metal lever at the left of the module and lift the module straight up by its edges without bending the pins.

The jumper block at J16, next to the battery, must match the module: red 233 MHz, white 266 MHz, black 300 MHz. Fit it with the gold pins facing down, covering the pins Apple shows. A missing or wrong block leaves a computer that does not start. Apple covers the block with a warranty sticker. Low End Mac warns that a G4 upgrade must be made for the 66 MHz bus; G4 modules from 100 MHz-bus machines do not work properly in the beige G3.

Voltage regulator card

The processor's supply comes from a separate regulator card, 922-3292, that plugs into the logic board. Apple's first action for a machine whose fan runs with no chime, LED or video is to reseat this card, and to replace it before the logic board. Two capacitor values have been reported for these cards (4 × 1500 µF 6.3 V and, on a "Switch Power" card 614-0081, 4 × 680 µF 10 V); see Power Macintosh G3 (Beige) Capacitor Replacement Guide.

Power supply

In the desktop the supply sits in the back right corner of the internal chassis as you face the computer. Open the case, unplug the supply's cables from the CD-ROM or DVD-ROM drive, the hard drive and the logic board, and take out the two screws on the back panel. Set the voltage switch on a replacement before plugging it in (115 V in the US).

The desktop and minitower supplies are different, and jumper J28 on the logic board must match: "Mac" for the desktop supply, "PS" for the minitower. A board moved between cases without moving the jumper will not start.

Drives

• The board has two ATA connectors. A single device must go on J9, the connector nearer the rear panel; a device alone on J10 may not boot.
• Later boards support two devices (master and slave) on a channel; early machines do not.
• Low End Mac advises keeping the first partition of an ATA drive larger than 8 GB under 8 GB, with all system files inside it, and notes that drives over 128 GB need a third-party driver or a PCI controller.
• Hard drives shipped with the version 2 board (661-2063) are formatted HFS+. Do not run Norton Utilities 3.5.1 or earlier on them; Apple recommends the Disk First Aid on the machine's own system CD.
• See Hard Drive Maintenance and Repair and Floppy Drive Repair.

Cards and connectors

Clean dirty gold fingers on a PCI or I/O card gently with a pencil eraser after checking them under a magnifier. The PCI slots take three 15 W cards or two 25 W cards.

Removing the logic board

Open the case, then take out any PCI cards, the I/O card and, if the board is being replaced, the processor module. Swing open the expansion card cover, unplug all cables, remove the screw inside the top column support and the processor wire screw, press down the two tabs at the front of the board and slide it forward off them. Before fitting a replacement board, set J28 for the case, move the processor module and its jumper across and fit a new warranty sticker. Leave the voltage regulator and ROM DIMM on a board returned to Apple.

Related pages

• Power Macintosh G3 (Beige) Troubleshooting
• Power Macintosh G3 (Beige) Capacitor Replacement Guide
• Capacitor Failure Symptoms