Macintosh Quadra 900 General Maintenance

Macintosh Quadra 900

Maintenance guidance for the Macintosh Quadra 900. Apple services the Quadra 900, the Quadra 950 and the Apple Workgroup Server 95 in one manual, and they share the tower case, drive shelf and power supply bay.

Opening the machine

Unplug the machine and lay it on its side. Press the two latches, lift the cover and remove it; Apple warns that removing the cover with the machine standing may damage it.

Most work inside starts with the drive shelf: disconnect the floppy and SCSI data cables from the logic board (on an AWS 95 the SCSI cable goes to the PDS card) and the SCSI power cable from the power supply, remove the two drive shelf screws, slide the shelf towards the rear and lift it out by the cable tie and metal tab, keeping the cables clear of the case.

The power supply comes out after the drive shelf and the speaker bezel: disconnect the power supply cable from the logic board, remove the three mounting screws, remove the blank bezel, and lift the supply straight up by its two handles. The logic board then comes out after the expansion cards, the reset and interrupt switches and the keyswitch cable: press down on the latch, slide the board towards the front and lift it out front first. Unplug the computer before removing expansion cards; Apple warns that doing so with it plugged in can damage the logic board and cards.

Regular cleaning

• Blow dust out of the power supply, its fan and the logic board with compressed air.
• Keep the vents on the side and rear clear. Apple's first cure for intermittent shutdowns is to clear them: the thermal protection circuit can shut the system down, and it should work again after 30 to 40 minutes.
• Clean the mouse; Apple's chart for a cursor that does not move includes inspecting the inside of the mouse for dirt.
• For yellowed plastics see Retrobrite.

The floppy drive is the 1.4 MB SuperDrive. Apple recommends dust shields on SuperDrives in the Quadra 900; replacement drives ship with one fitted, and a drive must be cleaned before a shield is added. For cleaning and lubrication see Macintosh Floppy Drive Maintenance.

Keyswitch

The front-panel keyswitch has a secure position. Apple's symptom charts start the entries for a floppy drive that will not work or will not eject, a cursor that will not move, and a keyboard that does not respond by checking that the key is not set to secure. Check it before suspecting the hardware.

PRAM battery

The battery is a 3.6 V lithium cell in a latched holder on the logic board. Apple's check needs only the cover off:

1. Set the voltmeter to the 10 V DC scale.
2. Hold the positive probe to the positive end of the cell (marked "+" on the logic board) and the negative probe to the negative end.
3. If the cell reads below 3.2 V, replace it.

Replacing it is a bigger job: Apple's procedure removes the cover, the drive shelf and the power supply first, then the latch at the end of the holder is prised open with a small flat-blade screwdriver and the cell lifted out. Apple's charts also list a battery check for intermittent shutdowns.

If the cell has leaked, remove it and clean the board before powering it again. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Capacitors

The logic board is built with tantalum capacitors, according to Recap-a-Mac, so it does not have the leaking surface-mount electrolytics of later Macintosh boards. The aluminium electrolytics are in the power supply; see Macintosh Quadra 900 Capacitor Replacement Guide.

Connectors and sockets

Clean with a contact cleaner such as DeoxIT D5 and let it dry before powering on:

• the sixteen 30-pin RAM SIMM sockets, which take SIMMs in groups of four (Apple supports 1 MB and 4 MB SIMMs; 8 MB and 16 MB SIMMs work but are not supported by Apple);
• the VRAM SIMM sockets (100 ns or faster; four 256K or two 512K SIMMs for 2 MB);
• the five NuBus slots and the processor-direct slot;
• the power supply cable, the keyswitch cable and the drive cables.

Power supply

Apple's specification is 100-240 V AC RMS from a self-configuring supply, 50-60 Hz single phase, 303 W maximum not including the monitor. The Service Source has no voltage-adjustment procedure and no rail tolerance table; check the rails at a drive power connector against nominal and watch for a rail that sags when the drives spin up.

The fan is mounted on the power supply. To replace it, remove the supply, disconnect the fan cable from it and remove the four fan screws.

SCSI and hard drives

The Quadra 900 has one external DB-25 SCSI port and one internal 50-pin port, and supports up to eight devices including the computer, which is always ID 7. The AWS 95, and a Quadra 900 or 950 fitted with the Workgroup Server PDS card, have two internal and two external ports on four buses; the Mac OS supports only seven devices. The internal bus is terminated on the logic board, so internal drives must not carry terminators; Apple's chart for devices that work internally or externally but not both includes making sure the internal hard drives are not terminated.

Apple's procedure for preparing a replacement drive for a Quadra 900 or 950:

1. Remove the terminator resistors from the replacement drive. Apple's caution is that failing to remove them can damage the logic board. On the 160 MB drive they pull up by a tab; on the 230 MB drive they come out with needle-nose pliers.
2. Fit the drive in the customer's carrier with four screws, torqued to 8.0 in-lb in the sequence Apple shows. Apple warns that a drive not properly torqued to its carrier can be damaged.
3. Attach the SCSI select cable: tab up on the 160 MB drive, as shown in Apple's figure on the 230 MB drive, and tab down on the 400 MB drive.

For a drive that does not appear on the desktop, Apple's chart starts with checking SCSI IDs and updating the driver with HD SC Setup. See also Macintosh HDD Maintenance.

Specifications for reference

Item	Apple's figure
Size	8.9 in wide, 20.6 in deep (224 × 523 mm); height printed as "16.8 in. (473 mm)", where 473 mm is 18.6 in
Weight	36 lb 12 oz (16.7 kg) without a hard drive
Operating temperature	10-40 °C (50-104 °F)
Relative humidity	20-80 %, non-condensing

Related pages

• Macintosh Quadra 900
• Macintosh Quadra 900 Troubleshooting
• Macintosh Quadra 900 Capacitor Replacement Guide
• Macintosh Quadra 950
• Recommended Tools