Macintosh Quadra 650

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Centris 650
CPU: 25 MHz Motorola MC68040
RAM Type:72-pin SIMM
Maximum RAM: 138 MiB
Expansion slots: 040-PDS
3 NuBus
Supported OS: System 7.1 - Mac OS 8.1
A/UX 3.0.1 - 3.1.1
Introduced:February 10 1993
Discontinued:October 21 1993
MSRP:$2699 (US)
Full Specifications

Replacement for the ageing Quadra 700, the Centris (later Quadra) 650 might not have provided much of a speed boost but it did address the 700's biggest failing: expansion.


Along with the Quadra 900, the Quadra 700 had launched the flagship Quadra series in 1991. The new machines had put the power of the Motorola 68040 into the hands of users and they'd been very warmly received. Two years later and the pair were starting to look a little long in the tooth. The 950 had already been replaced by the Quadra 950 and, in February 1993, it was time for the 700 to drop off the product list.


When first released, the Quadra 700 had been one of Apple's top-of-the-range machines but that didn't mean that it wasn't without its problems. By re-using the case from the IIci the machine had no internal drive bays, which meant that there was no way for users to add the one device that was very quickly becoming a 'must have' — the CD-ROM drive. The 650 not only addressed this but also gave the old workhorse a bit of a shot in the arm at the same time.

Despite being initially launched under the Centris label, the 650 boasted a full-blown 68040 rather than the lower price/performance 68LC040 (which lacks the dedicated floating point unit) seen in the other Centris machines. (N.B. A limited number of the Centris machines did come fitted with the 68LC040 instead of the 68040. These machines also lacked on board Ethernet and came with only 4 MiB of on board RAM instead of 8 MiB.) Running at the same 25 MHz as the 700, the new machine might not have seemed like much of an improvement but by using interleaved 72-pin SIMMs, instead of 30-pin modules, users could see a 10% speed boost. The new and improved SCSI bus sped up disk access and the accelerated video made everything look great.


Quadra 650
CPU: 33 MHz Motorola MC68040
RAM Type:72-pin SIMM
Maximum RAM: 138 MiB
Expansion slots: 040-PDS
3 NuBus
Supported OS: System 7.1 - Mac OS 8.1
A/UX 3.0.1 - 3.1.1
Introduced:October 21 1993
Discontinued:September 12 1994
MSRP:$2399 (US)
Full Specifications

If this wasn't enough speed, users only had to wait eight months until the machine was rebranded as the Quadra 650. Everything was the same as before except that the machine was clocked at 33 MHz instead of 25 MHz...and costed $300 less.

Where both versions of the machine excelled over the older 700 was in the field of expansion and connectivity. The older machine had lacked any sort of internal drive bay — aside from the pre-filled single hard drive and floppy bays — and while there had been two NuBus slots and a PDS slot, there hadn't been any on board Ethernet — which used up a precious NuBus slot if users felt the need to add a NIC. The 650 had a spare 5.25" drive bay — which could be pre-filled with an optional CD drive (N.B. The 650, along with the Quadra 800, were the first Macs that could be booted directly from CD) — three NuBus slots instead of two, and an optional AAUI Ethernet interface.

Having taken the case from the IIvi may have certainly given the 650 the expansion options that were so desperately needed but it also re-introduced one of the most loathed cases in the history of the Mac. The steel case was very symbolic of the IBM PC and seemed to lack the warmth and friendliness that encapsulated the Mac. As an added 'bonus' the sharp metal edges make working inside the 650 something of a health hazard with it being all too easy to slice a finger, hand or foot and cause blood to enter the case.

Full Specifications

  • General
    • CPU: 33 MHz (25 MHz in Centris) Motorola MC68040 (68LC040 in some Centris machines)
    • ROM: 1 MiB
    • Bus Speed: 33 MHz (25 MHz in Centris)
    • Data Path: 32-bit
    • RAM Type: 72-pin SIMM (80 ns)
    • Standard RAM: 4 MiB - 8 MiB
    • RAM Onboard: 4 MiB - 8 MiB
    • RAM Slots: 4
    • Maximum RAM: 138 MiB
    • Cache: 8 KiB (L1)
  • I/O & Expansion
    • ADB: 2
    • Serial: 2
    • SCSI: 1 (DB-25)
    • Ethernet: 1 (AAUI) (optional)
    • Audio In: Mini-jack
    • Audio Out: 16-bit stereo 22 KHz (mini-jack)
    • PDS Slot Type: 040
    • NuBus Slots: 3
  • Storage
    • Hard Drive: 80 MiB - 500 MiB
    • Hard Drive Type: SCSI
    • Floppy Drive: One 1.44 MiB SuperDrive
    • Optical Drive: 1 (optional)
    • Optical Drive Type: CD-ROM (2x speed SCSI)
  • Video
    • Max Resolution: 512×384 (16-bit), 640×480, 800×600, 832×624 (8-bit), 640×480, 800×600, 832×624 (16-bit — 1 MiB), 832×624, 1024×768, 1152x870 (4-bit), 832×624, 1024×768, 1152×870 (8-bit — 1 MiB)
    • Standard VRAM: 512 KiB - 1 MiB
    • VRAM Slots: 2
    • Maximum VRAM: 1 MiB
    • Video Out: DB-15
  • Miscellaneous
    • Codename: Speedbump 650 (Quadra), Wombat 25 (Centris)
    • Gestalt ID: 36
    • PRAM Battery: 3.6V half-AA
    • Case Style: IIvi
    • Dimensions: 13.0" x 16.5" x 6.0" (W x D x H)
    • Weight: 25 lbs.
    • Mac OS Support: System 7.1 - Mac OS 8.1
    • A/UX Support: 3.0.1 - 3.1.1
    • Introduced: February 10 1993
    • Introduced: September 12 1994
    • MSRP: $2699 (Centris), $2399 (Quadra) (US)

Common Problems

Aztec Powersupply

There is a problem with some Aztec Powersupplies where the 5V trickle voltage circuit goes bad over time. The +5V.TRKL supply voltage for the power-on circuit, as fed to pin 10 of the (Macintosh IIcx/IIci/650) powersupply connector, is in the Aztec power supply generated on the top PCB (95402 A) with a circuit that (a.o.) consists of C34 (33 nF), Q5 and Q6 (transistors) and D15. This circuit forms a sawtooth oscillator (sawtooth voltage on C34), the output of which is fed to the transformer T4, in order to galvanically separate the trickle supply from the mains (the sawtooth generator is on the primary side !). The function of D15 is to compensate a voltage (junction) gap, but this compensation is critical, unfortunately. Therefore, the oscillator can end up in a stable, non oscillating state (minimum voltage over C34) and consequently no AC voltage on the secondary side of T4. Simply superimposing a trickle voltage (5 V, > 5 mA) on pin 10 of the power supply connector (or the ADB connector) does not work, because signals from the sawtooth oscillator are used in other places of the supply as well. The solution to the problem is to replace D15 by two silicon (signal) diodes, connected in series, thus doubling the voltage gap to 1.2 Volts. In that case, there is no stable non-oscillating state possible. In order to end up with (approximately) the original frequency (roughly 17 Khz), it might be considered to change C34 to 39 nF, but the value is by no means critical. The change, though simple and very cheap, requires some experience with electronics and at least a soldering iron. Please note that the primary DC voltages are high (hundreds of Volts) and remain present some time after the supply has been disconnected. Disconnect the computer, open it and remove the power supply (directions can be found on the internet). Remove the fan (latches on the bottom side). You may choose not to disconnect the fan, since the lock of the power connector (on the lower PCB) is hard to reach. Open the power supply by removing its top cover (two screws) and remove the top insulation sheet. Remove the two screws with which the top PCB is fastened, pull it (a little) towards the rear and lift it. Unplug the mains connector from the top PCB (lock is on the down side !) and rotate the PCB far enough to see D15. Unsolder D15 (entirely) and connect it in series another (similar) diode. Remount the duo and reverse the above steps (put everything together again). The startup of the IIcx/IIci/650 after this modification is always certain, but the startup delay depends on temperature. The colder the machine, the longer the delay.

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