Macintosh Centris 650 General Maintenance

Macintosh Centris 650 (photo: Benoît Prieur, CC0)

The Macintosh Centris 650 and the Macintosh Quadra 650 share a case, a logic board design and a power supply, and Apple documents them together in one Service Source volume. The maintenance notes below apply to both.

Specifications

Apple's specification

Item	Centris 650	Quadra 650
Processor	Motorola 68040 at 25 MHz	Motorola 68040 at 33 MHz
RAM	4 or 8 MB standard, expandable to 132 MB, 72-pin SIMMs
ROM	1 MB
PRAM	256 bytes of non-volatile parameter memory
VRAM	512 KB, expandable to 1 MB
Expansion	Three NuBus slots and one inline processor-direct slot
Ethernet	On-board Apple Ethernet port
Line voltage	100–240 V AC, 50–60 Hz
Maximum power	112 W, display excluded
Dimensions	6.0 × 13.0 × 16.5 in (152 × 330 × 419 mm), 25 lb (11.3 kg)

The developer note gives the maximum RAM as 132 MB with 4 MB on the logic board and 136 MB with 8 MB, and says the Centris 650 was also sold with a 68LC040, which has no FPU.

Power supply

Apple's service part number for the supply is 661-0758. Apple Rescue of Denver lists it as Apple 614-0009, 112 W, made by Delta (SMP-120EB) or ASTEC (AA16870), and fitted to the Centris and Quadra 650, IIvi, IIvx, Performa 600 and Power Macintosh 7100.

Apple's IIvx developer note gives the ratings of the IIvx supply:

Macintosh IIvx power supply ratings (Apple)

Load	+5 V	+5 V TRKL	+12 V	−12 V	Total
Minimum	1.5 A	0 A	200 mA	0 A	9.9 W
Maximum	15 A	1 mA	2.5 A	600 mA	112 W
Peak	15 A	1 mA	6 A (12 s maximum)	600 mA	130 W

The same note says the supply adapts automatically to 85–270 V AC, and that the +5 V trickle output is present whenever the computer is plugged in, powering the real-time clock, parameter RAM and ADB power-on circuit. The Centris developer note gives the Centris 650 supply as up to 112 W, with 1.5 A at +5 V and 2.0 A at +12 V left for internal drives after the logic board and cards.

Apple publishes no rail tolerances and no power-supply adjustment for the Centris 650 or Quadra 650; power faults in its symptom charts end at "Replace power supply". The "+5 V 4.85–5.15 V / +12 V 11.90–12.75 V" adjustment found on other pages belongs to the Macintosh 128K, 512K and Plus power/sweep board and does not apply here.

Working on the supply

The supply is mains-powered. With its cover off, its primary side is at mains potential while plugged in, and the reservoir capacitors stay charged after it is unplugged. Unplug it, discharge each reservoir capacitor through a resistor (1 kΩ, 5 W is suitable), and confirm with a meter before touching the primary side. A 68kMLA member's list for a Centris 650 supply gives C1 and C2 as a 470 µF 200 V pair; two 200 V parts on a supply that accepts 240 V mains (about 340 V DC once rectified) must be working as a series pair, so replace both together with matching parts and never fit a single 200 V capacitor in their place. The full list and procedure are on Macintosh Centris 650 Capacitor Replacement Guide.

Battery

A 3.6 V lithium battery keeps the clock and parameter RAM running while the machine is unplugged. Apple's check: set a meter to the 10 V DC range, put the positive probe on the positive end of the battery (marked "+" on the logic board) and the negative probe on the negative end, and replace the battery if it reads below 3.2 V. Apple's chart for a machine that shuts down intermittently includes this battery check, after checking the vents and the power cord.

Remove the battery before the machine goes into storage.

If it has leaked

Lithium battery leakage is neutralised with sodium bicarbonate, not vinegar (vinegar is for alkaline cells). Use a paste of bicarbonate and distilled water, rinse with distilled water, then isopropyl alcohol, and dry thoroughly. Inspect under magnification for traces that have gone dull, green or thin, check continuity along every track leading away from the holder, and look at the underside of the board. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Connectors and sockets

• Clean the DRAM and VRAM SIMM sockets with isopropyl alcohol on a swab and reseat the modules. Do not use an abrasive on gold contacts.
• Check the NuBus and processor-direct slots, and any card's edge contacts, for bent pins and debris.
• Look at the logic board power connector for browning or a distorted housing.
• Reseat the ADB, serial, SCSI and floppy connectors, and check ribbon cables for cracked conductors at their folds.

A contact cleaner such as DeoxIT D5 is for contacts that are actually corroded.

Capacitors

The logic board has no aluminium electrolytics. A 68kMLA member who worked on Centris 650 boards reports that the capacitors other than those in the supply are tantalum or ceramic, and Retro Viator found no electrolytics on a Quadra 650 logic board. These are community reports, not Apple statements; check your own board.

Solid tantalums most often fail short, pulling a rail down. Look for a cracked, split or scorched body, and with the supply disconnected check each rail for a short to ground. A tantalum's bar marks its positive end. Derate a replacement by 50 %: 10 V or more on the 5 V rail, 25 V on 12 V.

The power supply does contain aluminium electrolytics; see Macintosh Centris 650 Capacitor Replacement Guide.

Cleaning

Opening the case

Loosen the captive screw at the back (Apple cautions that excessive force on it damages the top cover), slide the cover about an inch towards the front without tilting it, and lift it straight up. When refitting, do not knock the reset/interrupt switch and light pipe out of alignment.

Inside

• Use compressed air and an anti-static brush on the logic board, the power supply and its fan. Hold the fan still while blowing it out.
• Use isopropyl alcohol and a soft brush for grime, particularly around the battery holder.
• Check the underside of the logic board as well as the top.

Outside

• Clean the case with a damp microfibre cloth and mild detergent; no abrasives or solvents.
• ADB keyboards can be dismantled for washing: keycaps off, warm soapy water, dry completely, then clean the contacts with isopropyl alcohol.
• Take the mouse ball out and clean the rollers with isopropyl alcohol.

The yellowing of the grey plastics is in the body of the plastic and does not wash off; see Retrobrite.

Floppy drive

The 1.4 MB Apple SuperDrive is a direct-drive mechanism with no belt. If a disk will not eject, Apple's first step is to switch off and hold the mouse button down while switching on; the next is to eject it manually. Clean the heads with isopropyl alcohol on a lint-free swab, supporting the upper head arm. See Macintosh Floppy Drive Maintenance and Floppy Drive Repair.

Hard disk

The drive at the end of the internal SCSI cable must be terminated and other internal drives must not; the logic board terminates the external end automatically when no external device is attached. The computer is always SCSI device 7. SCSI-to-SD adapters such as BlueSCSI, ZuluSCSI and SCSI2SD can replace an original drive. See Macintosh HDD Maintenance and Hard Drive Maintenance and Repair.

Cooling

Keep the vents and the power-supply fan clear. Apple's chart for a machine that shuts down intermittently starts with the air vents: thermal protection circuitry may shut the system down, and it should be usable again after 30 to 40 minutes.

Storage

• Remove the battery.
• Store the machine dry and at room temperature.
• If the logic board is out, keep it flat in an anti-static bag.

Related pages

• Macintosh Centris 650
• Macintosh Centris 650 Capacitor Replacement Guide
• Macintosh Centris 650 Troubleshooting
• Macintosh Quadra 650
• Centris 650/Quadra 650 Service Source
• Macintosh Centris 610 Centris 650 and Quadra 800 Developer Note
• Recommended Tools