Macintosh Centris 650 Troubleshooting
Troubleshooting is essential for diagnosing and resolving issues with your Macintosh Centris 650 (and Quadra 650). This guide covers the most common problems encountered with these systems.
Note: The Centris 650 and Quadra 650 share the same hardware, so this guide applies to both models.
Preliminary Checks and Power Supply Basics
Before detailed troubleshooting, verify:
- Power cable is securely connected
- Wall outlet is functional (test with another device)
- Power switch on the rear is in the ON position
- No visible damage to the power cord
Expected Voltages
| Rail | Expected Range |
|---|---|
| +5V | 4.85V – 5.15V |
| +12V | 11.9V – 12.7V |
| -12V | -11.9V – -12.7V |
No Power (Unit Dead)
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| No response when power button pressed | Dead power supply | Test PSU voltages; check/replace PSU capacitors |
| No response | Failed PRAM battery | Replace 3.6V lithium battery |
| No response | Shorted tantalum capacitor | Inspect logic board for burn marks; replace failed cap |
| Clicking sound from PSU | PSU overload protection triggering | Disconnect all drives and cards; test bare system |
| PSU fan spins briefly then stops | PSU capacitor failure | Recap power supply |
| Burning smell | Component failure | Immediately unplug; inspect for burnt components |
Power Supply Troubleshooting
The Centris/Quadra 650 power supply contains electrolytic capacitors that degrade over time. Common failures include:
- Bulging or leaking capacitors
- Dry joints on high-current connections
- Failed rectifier diodes
Warning: Discharge the power supply before servicing. High-voltage capacitors can retain charge.
Startup Chime but No Video
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Chime, no video on internal video | VRAM issue | Reseat or replace VRAM SIMMs |
| Chime, no video | Monitor not connected properly | Check video cable and adapter |
| Chime, no video | Monitor settings | Try different resolution sense pins |
| Chime, no video | Logic board video failure | Test with NuBus video card |
Video Resolution Sense Pins
The Centris/Quadra 650 detects monitor resolution via sense pins on the DB-15 video connector. If using a modern monitor with an adapter, ensure proper sense pin configuration for your desired resolution.
No Startup Chime
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Power light on, no chime | RAM failure | Reseat SIMMs; test with known good RAM |
| Power light on, no chime | ROM SIMM issue | Reseat ROM SIMM |
| Power light on, no chime | Logic board failure | Test with minimal configuration |
| No power light, no chime | Power supply failure | Test PSU; recap if needed |
Sad Mac Error Codes
If the system displays a Sad Mac icon with an error code, see the Sad Mac Error Codes page for a full list.
Common codes for the Centris/Quadra 650:
| Code | Meaning |
|---|---|
| 0000000F | ROM checksum failure |
| 000000XX (01-05) | RAM test failure (bank indicated by XX) |
| 0000000E | ROM SIMM error |
Intermittent Booting or Freezing
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Random freezes | Overheating | Clean dust; verify fan operation |
| Random freezes | Bad RAM | Run memory diagnostic; test SIMMs individually |
| Random freezes | Failing hard drive | Back up data; replace drive or use BlueSCSI |
| Freeze during disk access | SCSI termination issue | Verify termination at end of chain |
| Crashes after warmup | Thermal issue | Check thermal compound; verify cooling |
| Intermittent boot | Oxidized contacts | Clean SIMM slots and card slots with DeoxIT |
SCSI Issues
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Drive not recognized | SCSI ID conflict | Ensure unique IDs (0-6) for all devices |
| Drive not recognized | Bad SCSI cable | Replace internal SCSI ribbon cable |
| System hangs at startup | Missing termination | Add terminator to last device in chain |
| Intermittent disk errors | Loose connection | Reseat SCSI cables |
| Blinking question mark | No bootable system | Install System software; check drive |
SCSI ID Notes:
- Internal drives typically use ID 0
- CD-ROM often uses ID 3
- External devices: ID 1-6
- Host adapter is always ID 7
- Termination required at the end of the chain
Floppy Drive Issues
See: Macintosh Floppy Drive Maintenance
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Won't read disks | Dirty heads | Clean heads with cleaning disk |
| Won't eject | Mechanical failure | Manual eject with paperclip; service drive |
| Disks unreadable | Worn drive heads | Replace floppy drive |
| Grinding noise | Dried lubricant | Lubricate drive mechanism |
Ethernet Issues (AAUI)
Some Centris 650 configurations include onboard Ethernet via AAUI-15 connector.
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| No network connection | Missing transceiver | Connect AAUI-to-10BaseT transceiver |
| Intermittent connection | Bad transceiver | Replace AAUI transceiver |
| No Ethernet option | No onboard Ethernet | Install NuBus Ethernet card |
NuBus Card Issues
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Card not recognized | Poor seating | Reseat card firmly |
| Card not recognized | Slot failure | Try different NuBus slot |
| System won't boot with card | Card conflict | Remove card; test system; reinstall |
| Intermittent issues | Oxidized contacts | Clean card edge connector |