Q630 (LC630, P630, P631, P635, P636, P638, P640) Speedup

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This is a modification that can be performed on a Quadra 630, LC630,
Performa 630, Performa 631, Performa 635, Performa 636, Performa 638, or
Performa 640 to speed it up to 40MHz.

Keep in mind that this will void your warranty. Dealers or Apple may refuse
to accept the board as an exchange in or out of warranty with this
modification.

Unlike the modifications outlined in the Mac Crystal Oscillator Speedup
History File I maintain where those computers use a TTL crystal oscillator
to clock the processor, the Quadra 630 uses a Clock Generator. This clock
generator is located at position U20 on the motherboard. Depending on the
surface mount resistors used, this part will either put out a signal for 25,
33, or 40MHz operation. Unlike the procedure used to clock chip many of the
other Macs, this procedure is not a "sure thing". This is partly because you
cannot back off just a little if you have problems at 40MHz. The statistics
at the bottom of the page will help you weigh the risks.
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There are four resistor pads used in this modification. Surface mount (SMT)
resistors are placed in these pads to pull "low" or "high". The pads are on
the bottom of the motherboard, and are in sets of two, so you need to have a
resistor on one of the first two and one of the second two. The resistors
are either 300 Ohms (301) or 4.7k Ohms (472). They are the "0805" surface
mount package.

                                Resistor Pads

       R153 (low) R149 (high) R155 (low) R156 (high) Pull       Speed

       301                    301                    low, low   25MHz

       301                               472         low, high  33MHz

                  472                    472         high, high 33MHz

                  472         301                    high, low  40MHz

The Quadra 630, LC630, P630, P635, P636, and P638 use the same motherboard.
The LC and Performa machines have a 33MHz 68LC040 processor instead of a
full 68040. Unlike the Q605 modification, the gestalt does not change at the
different speeds, so there are no software install problems, and there will
never be any software install problems on a modified 63x machine in the
future.

To do the modification to go from 33 to 40MHz, a 21% speedup, you just need
to swap some resistors. The resistors have been glued onto the board prior
to soldering, so you need to heat both sides of the SMT resistor at the same
time with two soldering irons, and lift the resistor off with the irons.
This will break the glue's bond to the SMT resistor. To solder on the
resistor, place it on the pads (it does not matter which way it faces), hold
it there with a small screw driver, and solder one side to the board at a
time.

The modification:

  1. remove the SMT resistor from R153, and solder it onto R155
  2. remove the SMT resistor from R156, and solder it onto R149

That's it.

Here's a picture of the bottom of a Q630 board and the location of the
resistors:

[Image]
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Keep in mind however that the 33MHz 68040 will now be running at 40MHz. The
part is not rated to run at these speeds, but my experience shows that this
will not be a problem.
You will also want to place a heat sink on the 68040. You have plenty of
space, so any of those heatsinks will do. There is no need for an additional
fan since the Apple fan blows air right over the processor.
The Valkyrie (video) chip also gets pretty warm, so you should attach a
small heatsink to it as well. The one I used was 28 x 26 x 15mm.

Here's a picture of the top of a Q630 board with heatsinks on the 68040 and
Valkyrie chips:

[Image]
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There are some Speedometer 4.0 Files for a Q630 at 25, 33, and 40MHz on the
Clock Chipping Home Page you may want to check out.

At 25, 33 and 40MHz I have checked the serial ports, video, floppy drive,
IDE drives, and RAM, and have observed no problems.

I've now heard of several cases where Apple PPC cards worked fine in
modified Q630s, so it looks like the PPC card will work at 80MHz.
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A question has been raised as to the success of this modification. If you
perform this modification on a 630, please fill out this form (or e-mail me
if your www browser does not support forms) and let me know if you have any
video problems. I would also like to know if you have placed a heatsink on
the 68040, and the Valkyrie chip. Your name will not be logged unless you
input it, but it might be useful for me if I have questions for you.

Name (optional):
E-mail (optional):
Video Problems:
Heatsink on 68040:
Heatsink on Valkrie chip:



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Here are the results of the above survey as of November 2, 1995

(Please come back and fill in the form after you do the modification so we
can get some statistics)

 Heatsinks Video Okay Video Problems

 None      15         2

 68040     12         1

 Valkyrie  0          0

 Both      18         4

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                              Marc Schrier
                              schrier@garnet.berkeley.edu