Macintosh Quadra 900 Troubleshooting

Macintosh Quadra 900 (Dusza Artysty, Wikimedia Commons, CC BY-SA 4.0)

Fault-finding for the Macintosh Quadra 900, built on the symptom charts in Apple's Macintosh Quadra 900/950/AWS 95 Service Source. The Macintosh Quadra 950 and Workgroup Server 95 share the case, power supply and manual, so the same charts apply. Apple lists the cures in order of likelihood: try the first, and if a replacement module does not cure the fault, refit the original before trying the next cure.

Before you start

• The front keyswitch: Apple's charts for a dead floppy drive, a disk that will not eject, a frozen cursor and an unresponsive keyboard all begin by checking that it is not set to Secure.
• The power supply is self-configuring for 100–240 V AC, 50–60 Hz, and is rated at 303 W maximum, not including the monitor. Apple's manual for these machines has no adjustments chapter and gives no rail limits.
• Remove NuBus and PDS cards and disconnect external SCSI devices when chasing a startup fault; Apple's video charts move or remove video cards as an early step.
• Check the PRAM battery (below).

Error chords at startup

Apple's charts describe Quadra 900 startup faults by the error chord played:

Symptom	Apple's cures, in order
One-part error chord during startup	Disconnect the SCSI data cable from the logic board and restart: if startup is then normal, initialise the hard disk; if the error chord still sounds, replace the hard disk. Disconnect the floppy drive cable and restart: if startup is normal, replace the floppy drive. Otherwise replace the logic board, keeping the customer's SIMMs
Two-part error chord during startup	SIMM verification (Apple's separate memory manual): check SIMM type, speed and grouping

The SIMMs must be 80 ns or faster and go in groups of four identical SIMMs. For Sad Mac codes on other Macintosh models see Sad Mac Error Codes.

System problems

Symptom	Apple's cures, in order
Does not power on: screen black, fan not running, LED off	Check the power cables; plug the monitor into the wall and check it has power; power cord; power supply; logic board
Clicking, chirping or thumping	Power supply; logic board; floppy drive cable; floppy drive
Shuts down intermittently	Clear the air vents on the side and rear: thermal protection may shut the system down, and it should recover after 30 to 40 minutes. Then power cord; check the battery; power supply; logic board
Crashes or hangs intermittently	Check the system software version and that the software is known-good and System 7 compatible; clear PRAM (Command-Option-P-R at startup, before "Welcome to Macintosh"); replace SIMMs; logic board; power supply

Video

Symptom	Apple's cures, in order
Screen black; sound and drives work; fan running; LED lit	Monitor brightness; monitor; video cable; move a video card to another slot; replace the video card; clear PRAM; SIMMs; logic board; power supply
Screen black; sound and drives do not work; fan running; LED lit	Video cable; move a video card; replace the video card; SIMMs; logic board; power supply
Screen partly or wholly bright, sound present, no picture	Monitor; video cable; move a video card; replace the video card; clear PRAM; logic board

The built-in video has 1 MB of VRAM on the board, expandable to 2 MB with four 256K or two 512K VRAM SIMMs of 100 ns or faster.

Floppy drive

Symptom	Apple's cures, in order
Internal floppy drive does not work	Keyswitch not on Secure; known-good disk; floppy cable; floppy drive; logic board; power supply
Disk ejects at startup and a blinking "X" appears	Known-good system disk; clear PRAM; floppy cable; floppy drive; logic board
Will not eject	Keyswitch not on Secure; hold the mouse button down while switching on; floppy drive; floppy cable; logic board
Tries to eject but the disk does not come out	Push the disk fully in; reseat the floppy bezel and drive so the slot lines up; eject manually; floppy drive
Runs continuously	Known-good system disk; floppy cable; floppy drive; logic board

See Macintosh Floppy Drive Maintenance and Floppy Drive Repair.

Hard disk and SCSI

Symptom	Apple's cures, in order
One internal hard disk does not spin	Hard disk data cable; hard disk power cable; hard disk
No internal hard disk works	Check for duplicate SCSI IDs; data cable; power supply; logic board
Drive does not appear on the desktop	Duplicate IDs; update the driver with Apple HD SC Setup and run Disk First Aid; SCSI cable; initialise if needed; try a known-good drive, then the logic board
Internal or external SCSI works, but not both	Duplicate IDs; terminator on the external device; make sure internal hard disks are not terminated; the external device's own manual

The internal SCSI bus is terminated on the logic board, which is why internal drives must not carry termination. Under System 7.0 and 7.1 the internal and external buses are treated as one, so every device on both needs a unique ID. See Macintosh HDD Maintenance and Hard Drive Maintenance and Repair.

Keyboard, mouse, printing and sound

Symptom	Apple's cures, in order
Cursor does not move	Keyswitch not on Secure; mouse connection; clean the mouse; move the mouse from the keyboard to the computer's ADB port (if it then works, replace the keyboard); mouse; logic board
Cursor moves but clicking does nothing	Mouse; logic board
Double-click does not open items	Remove duplicate System files; clear PRAM; then as for the cursor
No response from the keyboard	Keyswitch not on Secure; keyboard connection; keyboard cable; keyboard; logic board
Known-good serial or network printer will not print	System 7.0.1 or later; Chooser and control panel settings; printer cable; logic board
No sound from the speaker	Volume at 1 or above in the Sound control panel; speaker; logic board

PRAM battery

The clock chip is backed by a lithium battery that Apple rated for seven years. EveryMac gives it as 3.6 V lithium. Apple's test: with the cover off, set the meter to the 10 V DC range, put the positive probe on the end marked "+" on the logic board, and replace the battery if it reads below 3.2 V. To reach it, remove the cover, drive shelf and power supply, pry open the latch at the end of the holder and lift off the cover. Apple lists the battery among the checks for intermittent shutdowns.

Old lithium cells leak, and the leakage corrodes the logic board. Remove the battery from a machine going into storage. Neutralise leakage with bicarbonate of soda, not vinegar, and repair corroded traces before further fault-finding. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Capacitors

The logic board is built with tantalum capacitors and a working board needs none replaced; the aluminium electrolytics are in the power supply. Removing the supply, and the leaking input-board capacitors one owner found in a Quadra 950 supply, are covered on Macintosh Quadra 900 Capacitor Replacement Guide; general signs are on Capacitor Failure Symptoms.

Related pages

• Macintosh Quadra 900
• Macintosh Quadra 950
• Macintosh Quadra 900 General Maintenance
• Macintosh Quadra 900 Capacitor Replacement Guide
• Macintosh Quadra 900/950/ AWS 95 Service Source
• Macintosh Floppy Drive Maintenance