Mac Crystal Oscillator Speedup

From Higher Intellect Wiki
Jump to: navigation, search

Mac Crystal Oscillator Speedup History 2.3                April 1994

There has been a great deal of interest expressed over the net about 
these simple and inexpensive Macintosh modifications that yield 20-
40% speed increases.  Over the last year or so I have been doing a 
fair amount of crystal oscillator swapping/acceleration on Mac's, 
and gathering information from others.  I've made several posts to 
comp.sys.mac.hardware with the bulk of this info and as new 
machines come out, and new concerns surface, I will try to add them 
to this history of the modifications, post them on 
comp.sys.mac.hardware and make them available for anonymous ftp 
on in /info-mac/info/hdwr.  Included in this 
version is some of the news on the PowerMac's and Marlin Prowell's 
new C650 modification.

A little background:
All computers operate at a certain frequency with which operations 
are performed.  Within a certain class of computers, for example 
Mac's with a 68030 processor, the higher the frequency, the higher 
frequency of operations processed, and the faster the computer 
provided there is no other speed effecting hardware like a cache or 
slow data path.  The designer of the computer, Apple in this case,
will use components that are rated at the same frequency or faster 
than the final computer will be.  The 68030's are made by Motorola.  
All 68030's are generally alike in what they do, but they are not 
alike in how fast they can do it.  Motorola sells several 68030 
processors rated at 16, 20, 25, 33, 40 and 50MHz for Mac's, 
accelerators and such.  A large frequency difference will require a 
different mask during production of the processor, but small changes 
may not.  Motorola only needs to guarantee that the chip they mark 
as 20MHz will function properly at 20MHz under a variety of 
conditions.  Some chip vendors will test parts at different 
frequencies and sort the chips accordingly while others may just 
label the them at will and sell the chips at the different price as 
long as they are within spec.  So it is possible that the 20 and 25's 
actually come from the same batch, are separated on demand, and 
tested to make sure they will withstand that frequency.  Because of 
this, it is possible that a 20MHz processor will function fine at a 
higher frequency, say 25MHz.  Running it faster will however 
generate more heat.  

Many of the components in the computer need to be synchronized, so 
a frequency is generated by a crystal oscillator to synchronize them.  
Other parts like NuBus cards and video do not have to be the same 
frequency, so they may have separate crystal oscillators.  A typical 
computer may have several crystal oscillators to clock different 
groups of components on the motherboard.  Provided the components 
that are clocked by a particular crystal oscillator are capable of a 
speed increase, that crystal oscillator may be replaced with one of a 
higher frequency.  How much a specific Mac can be sped up by this 
method depends on how the motherboard was designed, the 
components used, and what things the crystal oscillator that 
controls the processor also controls.  With some of the newer Mac's, 
there are a few MHz differences in the top speeds reported for the 
same model, so part of this is luck of the draw.

This crystal oscillator swapping has been done for years, and some 
early computers even had jumpers that made it really easy to 
disable one oscillator and enable another higher frequency one.  The 
first Mac's to be modified were the IIsi's.  A stock IIsi's runs at 
20MHz, and IIci's at 25MHz, and since the architecture of these 
machines was so similar it seemed reasonable to run a IIsi at IIci 
speeds.  Another important factor was that earlier Mac's had just 
one crystal oscillator that controlled everything, and if you replaced 
it you would mess things up.  The IIsi was different as some noted 
through its frequency deviation from its 8 and 16MHz precursors 
where the main frequency was halved and quartered to run the CPU, 
serial ports, video...  The IIsi was different, it had 4 crystal 
oscillators, only one of which controlled the processor speed.

The Crystal Oscillator:
The type of crystal oscillator in the early Mac's is a full size, 14 pin 
package, TTL type crystal oscillator.  It is a rectangular metal can, 
with approximate dimensions of 2.0 x 1.3cm and typically about 0.3-
0.6cm high.  All crystal oscillators have 4 pins.  Some are numbered 
1,2,3,4 and others 1,7,8,14.  Pin 1 is always the pin next to the 
pointed edge (the others are rounded), with the dot, or next to the 
indentation on the newer CMOS, or surface mount crystal oscillators.  
With the pins facing down, put the dot, or indentation to your left, 
and the pin on the left, closest to you is pin 1.  Going counter 
clockwise, pin 2 (or 7, depending on what numbering scheme) is to 
the right, Pin 3(8) right side and further away, and 4(14) left side, 
and further away.  Pin 1 on all the newer Mac's with surface mount 
crystal oscillators, and some of the older ones is an output 
enable/disable pin (OE).  On some of the crystal oscillators you 
purchase Pin 1 will be OE, yet on many it will not be used (no 
contact (NC)).  It is not important which you get as you will not be 
using the output enable feature.  Pin 2(7) is a ground.  Pin 3(8) is the 
output.  Pin 4(14) is the supply voltage, +5 VDC.  I've checked a few 
of the older type Mac's, and the oscillator on Mac Plus's is not OE, 
while the ones on the IIsi's and Quadra 700's are OE.  I'm not sure 
why Apple uses these type of oscillators instead of the ones where 
pin 1 is not used.  I guess it is possible that something on the circuit 
board can ground pin 1 and stop or restart the computer.  If anyone 
knows, please let me know.  Printed on the crystal oscillator will be 
its manufacturer, part numbers, and frequency.  On these early Mac's, 
the processor runs at half the speed of the oscillator, so a 20MHz 
Mac IIsi has a 40MHz crystal oscillator.  

There are several different modification techniques.  They will all 
give you the same final max speed.  Some are just easier or more 
elegant than others.  As with all these modifications, even though 
there may be no visible sign that you modified your Mac, you have 
voided the warranty on the Mac.  As Apple states:

"This warranty does not apply if the product has been damaged by 
accident, abuse, misuse, or misapplication; if the product has been 
modified without the written permission of Apple; or if any Apple 
serial number has been removed or defaced."

This is what I seem to be finding.  These numbers vary from Mac to 
Mac, so these are just averages.  Some machines will go faster than 
this.  These are the oscillators that Output Enablers ships in their 


Machine   Mod-1   Mod-2   Mod-3   Oscillator/speed   Final Oscillator/speed
IIsi      yes     yes     no      40/20              55/27.5MHz
C610      yes     no      yes     10/20              14-14.31818/28.6MHz
C650      yes     no      yes     12.5/25            14.31818-14.75/29.5MHz
C650-mod  yes     no      yes     12.5/25            20/40MHz
C660av    yes     no      yes     12.5/25            16-17.496/35MHz
Q610      yes     no      yes     12.5/25            15-15.288/30.6MHz
Q650      yes     no      yes     16.6667/33.3       21-22/44MHz
Q660av    yes     no      yes     12.5/25            16-17.496/35MHz
Q700      yes     yes     no      50/25              70/35MHz
Q800      yes     no      yes     16.6667/33.3       20-21/42MHz
Q840av    yes     no      yes     20/40              23.247-24/48MHz
Q900      yes     yes     no      50/25              70/35MHz
Q950      yes     yes     no      66/33              ?75-80/?40MHz
PM6100    yes     no      yes     30/60              40/80MHz
PM7100    yes     no      yes     33/66              ?45/?90MHz
PM8100    yes     no      yes     40/80              ?50/?100MHz


The basic idea of Modification #1 is removing the onboard oscillator, 
and replacing it with a faster one.  This is the mod most people use 
on the IIsi, Q700, Q900, & Q950.

The basic procedure used is that you have to unsolder the TTL 
crystal oscillator from the motherboard on the Mac, and put in a new 
one.  Instead of putting one straight onto the board, it is nice to use 
a socket so you can test your individual Mac, and see what the cutoff 
frequency is, and you can always put the original oscillator back in 
the socket.

First find the crystal oscillator by referring to the previous table 
and description of physical characteristics.  Be careful when you 
remove the oscillator.  Most people just use a normal soldering iron, 
and are fine; a grounded (three prong soldering iron) would be a bit 
safer.  They just use copper wick to soak up the solder from all four 
pins, and pop out the proper oscillator.  Because the boards are 
multilayer, be careful not to damage anything; be gentle.  There was 
recently one report of a guy who damaged his IIsi board doing this.  
But that was the only incident I had ever heard of, and lots and lots 
of people have done this.  I use a "desoldering iron".  They melt the 
solder, and have a pump to suck out the solder while you swirl the 
pin from the oscillator around to get all the solder out.  After you 
have done all 4, if you have done a good job, the oscillator just pops 
out.  If you have access to one of these desoldering irons, I highly 
suggest you use it as it does a cleaner job, and there is less risk of 
burning (discoloring) the board.  Next, take a 14 pin IC socket, 
remove all the pins but 1,7,8, and 14, and solder it into the board 
(see Modification #3 for a Digi-key part number).  Make sure you put 
it in so pin 1 will go into pin 1, 2-2, 3-3, 4-4.  And the notch in the 
socket should face the same way the dot on the old oscillator was 
facing.  Now just put in a faster oscillator.

I have done this to a few IIsi, and the highest frequency we could get 
to work without problems was 27.5MHz.  Thus a speed increase from 
20 to 27.5MHz.  The actual crystal is 55MHz (double the frequency).  
TTL 55MHz crystal oscillators do exist, but they are rare.  The thing 
most people seem to do is get a CMOS oscillator, and they work just 
fine.  Digi-Key sells a 55MHz CMOS crystal oscillator in a 14 pin 
package, part# SE1509.  At 58.9 and above, there are problems with 
the floppy drive; you cannot boot the Mac from a floppy, but other 
than that it is fine until just over 30MHz.  I recently had a IIsi at 
28.3MHz and it was fine.  Be warned that some cards may not work 
after this modification.  Most will work at 25MHz, but will not at 
27.5MHz, so just stick with 25MHz if that is the case.

The IIsi does not come with a heatsink, so to reduce the heat in the 
processor, get a small heat sink to attach to the 68030 to cool it 
down; any heat sink will do; the more surface area the faster heat 
will be dissipated.  Be careful when you put on the heat sink.  
Typically you'll use some heat transfer grease, but the heat sink can 
slide off if the Mac is moved, and the heat sink might short 
something out.  The best thing seems to be to get a heat sink with a 
hole in the middle, or drill one yourself, use the heat transfer 
grease, but also put a small drop of super glue through the hole in 
the heat sink onto the chip or put a drop on the side, and this should 
hold it in place.  Fry's sells nice heat sink/fan combo's.  They run $10 
and up, and I think they are more than you need, but it should keep 
the processor cooler.  I believe they come with a Y cable to tap into 
your hard drive power cable to power the fan.  A more complete FAQ 
on this modification for a IIsi is available via anonymous ftp from in info-mac/info/hdwr (iisi-25mhz-upgrade-

For the Quadra 700 and 900, you can get 70MHz TTL crystals from 
Fry's.  The 70MHz may not work, and you may have to back down to 
66.6666MHz, the next most common frequency, Digi-Key part# 
CTX137.  The Q700, Q900, and Q950 come with a heatsink installed.  
A more complete file on this modification for a Quadra 700 is also 
available via anonymous ftp from in info-
mac/info/hdwr (quadra-700-clock-mod-145.txt).

It has been reported for, but I have not yet done a Q950, but the 
general idea is the same.  If anyone has any more info on doing a 
Q950, please e-mail me and I'll add it.


The basic idea of Modification #2 is to disable the onboard 
oscillator with a jumper and feed in a new signal on the back of the 
board.  There are very few who have performed this mod, but I feel it 
is more elegant and safer since you don't have to remove the onboard 
oscillator.  This newer, and less evasive method has been performed 
on IIsi's & Q700's by myself, and should work fine on the Q900 & 

The most difficult and risky part of "Mod-1" above is the removal of 
the oscillator, and this is an alternative procedure that gets around 
that since the crystal oscillators Apple uses have pin 1 as OE.  On a 
crystal oscillator with pin 1 as OE, if you ground pin 1, you disable 
the output from pin 3(8), and you can feed a new signal into pin 3(8) 
without removing the original crystal oscillator.
Several months ago I performed this modification on a Quadra 700 by 
tacking (soldering) a jumper on the back of the motherboard between 
pins 1 and 2(7) of the 50MHz oscillator, and ran wires about 8 inches 
long each from pins 2(7), 3(8), and 4(14) to a 14 pin socket attached 
to the inside of the Q700 with pins in positions 7, 8, and 14.  Into 
this we placed a 70MHz crystal oscillator and the Mac ran fine at 
35MHz and is still doing fine.  This modification is nice in that it is 
a bit less risky as far as damage to the motherboard, but you have to 
be careful to use thin wires in order to make clean solder joints.  
With this modification you could remove the wires at a later date to 
return to the original configuration more cleanly.  I cannot say for 
sure if this will work on a Q900 or Q950 until I put one of those 
crystals on a scope, or actually try the modification, but am pretty 
sure it will.  If anyone has removed a crystal from a Q900 or Q950 
and still has it, I'd be glad to check it out and send it back to you.


The basic idea of modification #3 is building a clip that disables the 
onboard oscillator, and feeds in a new, faster signal.  The beauty of 
this modification over the others is that you do not have to do any 
soldering on the motherboard itself, just on the part you clip onto 
the surface mount crystal oscillator in your Mac.  This is the 
modification most people use on the C610, C650, C660av, Q610, 
Q650, Q660av, Q800, Q840av, PM6100, PM7100, PM8100.

The really neat thing about this came into play in February 1992 
when Apple released the Centris 610, 650, and Quadra 800.  In these 
machines and since, Apple has been using surface mount crystal 
oscillators.  Now that Apple was using surface mount crystal 
oscillators, there was plenty of accessible area on the metal tabs of 
the oscillator.  In June '93 Guy Kuo reported the first crystal swap 
of sorts on a Centris 610 to the net.  He soldered pins 3, 5, 10, and 
12 of a 14 pin socket directly onto the surface mount crystal 
oscillator.  Because the pins on a TTL type crystal oscillator are at 
positions 1, 7, 8, and 14, he made jumpers between pins 5-7, 8-10, 
and 12-14.  He disabled the on-board surface mount crystal 
oscillator with a jumper between 3-5.  Then put the new crystal in 
the socket.  This file is also available on SUMEX in info-
mac/info/hdwr (centris-610-clock-mod-11).
I was a little hesitant about soldering onto my new Quadra 800, so 
wrote to him a few days later about using a surface mount test clip, 
and asked his thoughts.  He suspected I could not find a reasonable 
test clip, but otherwise believed it would work.  A few days later 
the 3M surface mount test clip arrived, and the test clip worked 
perfectly.  I was running my Quadra 800 at 40MHz, with no problems, 
and best of all the modification was all contained in a simple little 
clip that could be removed without trace at will.  And thus the 
removable test clip approach was born.  My Q800 even worked at 
48MHz as long as I did not access the serial ports.  A few days later 
I got several crystals, and found the highest frequency on my Quadra 
800 to be 42.0MHz.  Since then I've tried it at 42.106MHz, and the 
serial ports did not work, so the cutoff for my Q800 was at 42.0MHz.  
If you never use your serial ports, 48MHz worked fine for me, while 
at 50MHz my Mac was not happy and would not boot.  

So if you are still interested, you will need a surface mount test 
clip; 3M and Pomona make them, and I prefer the 3M ones.  Make sure 
you get a surface mount test clip.  The I.C. test clips also work, but I 
prefer the surface mount SOIC (small outline integrated circuit) 
ones.  A 10, 12, 14, 16, or 18 pin clip will be fine.  I'd say go with a 
14 or 16 narrow or wide.

14 pin, part# 923650-14-ND  $6.58
16 pin, part# 923650-16-ND  $6.96

These are the part numbers for the ones with alloy leads; I used to 
recommend the gold coated ones, but the resistance/corrosion effect 
is minimal.

You will also need a 14 pin IC socket, there are plenty of types.  The 
machined pin ones are nice because you can pop out the pins that are 
not needed to get them out of the way since you only need three pins 
in the socket. 

14 pin IC socket w/tin pins, part# ED3114  $0.57

You will also need an oscillator (more on this later), a little wire, 
soldering iron, solder, and possibly heat sink depending on the 
machine.  For a C610, C660av, Q610, and Q660av you should add a 
heat sink, HS160-ND is the 0.600 inch one, and is plenty ($3.98).

The others already have heat sinks, and do not get too hot.  I had an 
extra fan with my Q800, but removed it, and it has been fine.  The 
heat sinks come with the clips needed to attach them to the chip.  
These are a bit of a pain, you just have to work at it for a while.  
There may be several ways to do it, but I just slide the clips on from 
the side.  Sometimes they fall off half way there, but eventually it 
works.  Some people have been using the heat sink/fan combo's.  I 
have not, but they seem to work fine as well.  The new Q610 and 
Q660av computers are based on a new mask of the 68040 that comes 
at 25MHz without a heatsink (There is an "H" after the '040 and 
before the "RC").  This is the same mask as the C660av and Q840av 
uses.  If you do the modification on them it would be best to add a 
heat sink.

How to put it all together:

Stand the clip so it's jaws are facing down, and the rows of pins go 
>From left to right, and call the closer row A and the further row B.  
Number the pins from left to right 1 through 7 (for the 14 pin clip).  
Next place the IC socket with the pins down, and the notch to the 
left, and number the pins as 1, 2, 3, 4, 5, 6, 7 in the row closest to 
you, going left to right.  The other row is numbered 8, 9, 10, 11, 12, 
13, 14 as you go right to left (back towards the notch).
Now starting with the test clip, leave pins in positions A2, A6, B2, 
and B6.  Next solder a little jumper wire between pins A2 and A6.  
Now get the 14 pin IC socket, and remove all the pins but 7, 8, and 
14.  Solder a jumper wire from pin 7 on the IC socket to the 
jumpered pins on the clip, either A2 or A6.  Also solder a jumper 
wire from pin 8 to pin B6, and pin 14 to pin B2.
If you get the narrow clip, you may want to replace the spring with 
one with less tension; they are like $0.30 at hardware stores, and I 
cut them into two springs.  This way you don't have to push so hard, 
and it is easier to position on the motherboard.  Now put the crystal 
in the socket with pin 1 in 1, 2 in 2, 3 in 3 and 4 in 4.

There are several surface mount oscillators used on the 
motherboards.  The proper surface mount crystal oscillator on the 
mother board will have a frequency on it half that of your computer 
and can be determined from the above list.

That is it, now you just clamp it onto the surface mount crystal 
oscillator with the notch on the socket facing the same way as the 
surface mount crystal oscillator.  And watch to make sure the little 
pins clamp onto the surface mount chip.  You may want to use a 
flashlight for this.  These clips hang on very, very well, I've never 
had mine move in the last 9 months, nor any of the other ones I've 

Centris 610 Ethernet Problems:

Those Centris 610's that have ethernet capability share the 10MHz 
oscillator with the CPU.  If you replace that oscillator with a 
different one, your ethernet will no longer work.  In January, Eckart 
Hasselbrink ( posted a fairly simple 
hardware modification to fix this to comp.sys.mac.hardware.  So if 
you plan to use you ethernet on your Centris 650 and speed it up, you 
will need to perform Eckart's modification first.


I have only done PM6100's, and it works fine at 80MHz.  At 86MHz it 
overheats quite rapidly.  With a cool hairdryer cooling the heatsink 
on the 601, it worked fine, but was a bit noisy :-).  See the table to 
see which oscillator you will need to clip onto.  This mod should 
work just fine on the 7100 and 8100 computers as well.  On the 
8100 the power supply may be in the way of the clip.  If anyone in 
the Bay Area has a PM7100 or PM8100 and wants to try it, drop me a 
line and we can give it a spin.  Or if anyone tries it, please let me 
know how it goes so I can add it to this file and pass it on to others 
who ask.  The guesses on the chart about what oscillator to use for 
the PM7100 and PM8100 are just that, guesses.

On most of these newer machines, the problem is with the serial 
ports, but the speed of the memory is also important, so if you plan 
to boost your Mac very far, you may need faster SIMM's.

To test out the modification, the best thing to do is just use it a 
while.  You can run Speedometer 3.23 (available at SUMEX in info-
mac/cfg) to see the changes.  I use Snooper with the serial port 
loopback plugs to check the serial ports to find their limits; Snooper 
also tells you what frequency you are running at in round numbers.  
Snooper was made by Maxa, and I am told Snooper is currently owned 
by Central Point Software.  The current version of MacCheck is 1.0.5 
(available on, and it now properly reports the 
computer frequency.

If your Mac does not give the standard chime at startup it means 
your clip is only half on.  It is disabling the surface mount 
oscillator, but not replacing it.  Just remove the clip, reposition, and 
try again.

Special C650 Mod:

Using the above clips, the max frequency for a Centris 650 is about 
30MHz before you encounter serial port problems.  Marlin Prowell 
( following up on a hunch by James McPhail 
( looked into the differences between the C650 
and Q800 motherboards in hopes that a simple modification might 
enable the serial ports to function properly at 33MHz (Q800 normal 
frequency) or higher.  On the bottom of the motherboard, under the 
IOSB chip, Marlin found two differences.  R151 is installed on the 
C650's, and is missing on the Q800's.  R152 is missing on the C650's, 
and is installed on the Q800.  R151 is a 300 ohms resistor and R152 
is a 1.2k ohm resistor.  Looking at the bottom of the board, with the 
back away from you, R151 is 3 3/4" from the right, and 3" down.  The 
tabs for R152 are 4" from the right, and 3" down.  R151 is black, and 
says 301 on it.
Marlin felt that R151 was glued to the board, and just using solder 
braid he was unable to remove the resistor for fear that prying it off 
may damage the traces that run under it.  Heating the resistor with a 
soldering iron Marlin was eventually able to soften the glue and 
remove the resistor.  Or you can use James McPhail's two soldering 
iron Western technique with a soldering iron in each hand to heat 
each side simultaneously and flip the resistor off the board.  Now 
just add the R152.  Marlin suggests holding the surface mount 
resistor in place with a small screwdriver while soldering it to the 
exposed pads on the board.
Marlin has since used both the serial and modem ports error free 
while running his C650 at 40MHz, and MacCheck reports no problems.  
He has also checked to make sure the ethernet works, and it does.  
Since Marlin's initial modification, it has been confirmed by at least 
three people.  On some of these Mac's the CPU overheats after a 
while, so Marlin suggests you add a fan to dissipate the heat faster 
>From the heatsink.  You can also just run a bit slower, say 38MHz.  
You can purchase these 1.2k resistors from Digi-Key, but the 
minimum order is 200 of them.  If you e-mail your address to Output 
Enablers at, they will send you a free resistor left 
over from Marlin's extra 199.
****This modification makes your Mac think it has become a Quadra 
650, and the Quadra 650 did not exist when most of you purchased 
your Centris 650.  The System Enabler 040 that came with your 
Centris 650, version 1.0, will not work after this modification, and 
your Mac will not start up unless you have already updated the 
System Enabler 040 to version 1.1, the current version.  The System 
Enabler 040 version 1.1 is available from your local Apple Dealer, or 
you can ftp it from  Marlin suggests you also 
put the new enabler on all your recovery utility disks as well so you 
will be prepared next time something goes wrong.****

Recently a few companies have been started that replace the crystal 
oscillator in powerbooks to speed them up, and add a 68882.  I have 
some ideas on how to do this, and the precautions to make.  Has 
anyone done it themselves?  I have some info from Virgil Mehalek 
( who noted the differences between the 140 and 
170.  I'm not going to add that info until it has been attempted, but 
if anyone is interested in a copy of that info I can forward it to you.  
One important addition thanks to Virgil, worth noting now is that 
Active Electronics (800) 228-4836 sells the 33MHz MC68882-FN33A 
for $76.95 plus S&H.

Address' for some other parts suppliers:

Fry's Electronics
340 Portage Ave
Palo Alto, CA
(415) 496-6000

(800) 344-4539

Output Enablers
1678 Shattuck Ave.  Suite # 247
Berkeley, CA 94709

There are currently two companies that sell already made clip-on 
kits for the Mac's with surface mount crystal oscillators.

KS Labs
6326 E. Livingston Ave, Suite 131
Reynoldsburg, OH 43068

Output Enablers
1678 Shattuck Ave.  Suite # 247
Berkeley, CA 94709

If you have gotten any of these new machines to work, please let me 
know.  Or if you have any questions or comments that should be 
added to this, feel free to e-mail me as well.

                                           Marc Schrier

Disclaimer: I have been posting this info for quite some time, and I 
am now associated with Output Enablers.  I would like to continue to 
update and post this unbiased information as long as there is 
interest on the net.  Any opinions represented here are mine, not 
necessarily those of Output Enablers.

See Also

Share your opinion