From: gjohn@ostrich.Stanford.EDU (George John)
Subject: HOW TO UPGRADE YOUR IIsi TO 25MHz
Organization: Computer Science Department, Stanford University, CA, USA
Distribution: usa
Date: 8 Oct 92 02:30:05


HOW TO UPGRADE YOUR IIsi TO 25MHz

DISCLAIMER: Performing this upgrade WILL void your warranty.  It
involves desoldering an oscillator from the motherboard and replacing
it with a new one.  For all I know, performing this upgrade will fry
your CPU and people will sing songs about how dumb you were for doing
it for generations to come.  

Recently many people have been asking about how to speed up their
IIsi.  I upgraded my IIsi 2 or 3 weeks ago.  It cost me $4.  My
computer is now 25 to 50% faster.  I have had no problems with my
computer since then.  The upgrade involves desoldering the 40 MHz
oscillator and replacing it with a 50 MHz oscillator, thereby
increasing the speed of the CPU from 20MHz to 25MHz.  One of the big
things I've noticed is the graphics speedup -- graphics speed in 8
bits of color is faster now than monochrome was before!

Here's the story on performance.  Numbers below are speed relative
to a mac classic, so bigger is better:

				BEFORE		AFTER

CPU				5.24		6.69
Graphics			6.17		7.64
Disk				1.30		1.34
Math				5.45		6.91
Overall Performance		4.75		5.92  (25% faster as expected)

KWhetstones			6.33		7.97
Dhrystones			5.11		6.62
Towers				4.42		5.69
Quicksort			5.01		6.43
Bubble Sort			5.88		7.50
Queens				5.83		7.33
Puzzle				5.61		7.22
Permute				5.33		6.55
Fast Fourier			4.27		5.39
F.P. Matrix			4.53		5.70
Int. Matrix			4.85		6.09
Sieve				6.53		8.35
BENCHMARK AVG.			5.31		6.74

Graphics:
1 bit (mono)			1.72		2.15
2 bit				1.83		2.31
4 bit				1.92		2.47
8 bit (256 colors)		1.22		1.89 (50% FASTER!!!!)
Avg:				1.67		2.21


WHY THE UPGRADE WORKS:
	(I have not done the technical investigations myself -- I'm
just echoing previous reports I've seen on the net.)
	The IIsi was announced back in '90 as basically a poor man's
IIci.  The main difference is the lack of nubus slots inside.  If you
think about it, it makes engineering sense to reuse as much of the
IIci's design as possible.  I've heard that the chips that run off the
cpu clock were all designed for 25MHz performance for the IIci.  The
reason apple went with a 20MHz cpu in the si seems to be mostly
marketing -- would you buy a ci for $3500 if you could buy a 25MHz si
for $500 or $1000 less?  So it seems that the si was "crippled" for
marketing reasons by putting in a 40MHz oscillator package, thus
making the cpu run at 20MHz instead of the ci's 25MHz.
	Again, I have no idea whether the above paragraph has any
basis in fact.  It's just what I've heard.  For all I know, the IIsi
chips were designed to run at 20MHz which resulted in considerable
savings which was passed on to the consumer.  All I can say is that
my computer has worked okay for the last few weeks at 25 MHz.  It's
usually on at least 6-8 hours per day.


DETAILS ON THE UPGRADE:
Upgrading your machine is a pretty simple operation, if you've used
a soldering iron before.

Tools required: Soldering Iron.  And something small to pry with.

Parts required: 50MHz oscillator package, 4-pin socket (14-pin size
but just has pins in the 4 corners) for the oscillator (just in case
you want to be able to go back to 20MHz for some reason).  I bought
these parts at Fry's electronics in Palo Alto, CA.  The oscillator
costs $4, the socket was 11 cents.  The phone number for Fry's is
415-496-6000.  Don't know whether they do mail order or not.

Procedure:
Take the motherboard out of the case.  This is kind of fun actually.  
The mac IIsi is a really well-designed machine from an assembly-time
standpoint.  No screwdriver involved in disassembly.

Open the case.  (It lifts off from the back.)  

Remove the floppy drive.  (Unplug it from the motherboard and lift it
out of the case while holding in the 2 small latches on the sides of
the floppy drive.)

Remove the hard drive.  (Same thing, unplug the scsi cable from the
motherboard and the power cable, then just lift it out.  In this case
the latches on the case need to be pushed out so you can remove the 
drive.)

Remove the fan.  (You have to squeeze the plastic on the sides near
the bottom and back of the case to get it out.  Just lift it up while
squeezing.)

Remove the power supply.  (Again, just lift up while holding the two
latches in on the sides of the ps case.)  

Remove the simms.  (They snap out easily.  Again there are little
metal latches that hold them in place.)

Remove the motherboard.  (Pull it towards the front of the case while
pushing the two tabs on the case that hold it in place to the outside.)

Warning:  The soldering iron stuff comes next.  Fooling around with
your IIsi motherboard is not a good first soldering-iron project.
You can do all sorts of awful things to computer chips by making them
too hot, and soldering irons are kind of hot, sooo...

Desolder the 40MHz oscillator.  You should see a row of little silver
boxes just to the right of the simm slots.  The one closest to the
simms should say 40.000 MHz on it.  This is the guy to desolder.
You could really screw things up here, so be careful with the soldering
iron.  I removed mine by working on a pair of pins at a time -- get one
pin hot enough to melt the solder, then quickly switch to the adjacent 
pin and heat that pin while prying the oscillator away from the motherboard
on the other side.  Switch back and forth between the pair while prying
until one side has been completely detached from the motherboard, then
work on the other side.

Put the socket into the holes where the oscillator used to be.  This
is the same thing in reverse -- instead of prying off the old chip
you're pushing in the new socket.  I didn't want to bend the pins, so
I tried to push them all in just a bit at a time.  Warm up the solder
in one hole in the motherboard until it's melted and push that pin of
the socket in a bit, then repeat going around clockwise until the
socket is set firmly, all the way into the motherboard.

You're done.

You might want to put your 40MHz oscillator into the socket first,
just to make sure your computer still works.  Be sure to put it
back in the same way it was facing when you took it out.  On my
computer, all of the oscillators have 3 rounded corners and one 
square corner.  The square corners are all facing the bottom right
on my motherboard.  

Put the computer back together.  See if it works.

If it does, congratulations.  Pop the 40MHz crystal out of the socket
and put in the 50MHz crystal.  (Do this while the computer is off, of
course!)  Fire up your computer and run a benchmark.  Giggle like a
maniac.

Now, one concern of running the cpu 25% faster is that P=(I^2)/R 
(power equals current squared divided by resistance) and
we've just made increased the current by 25%, which will increase
the power by... well... at least 25%.  So the cpu will be getting
hotter and you might want to consider a heat sink.  These are big
metal weird-looking things designed to soak up heat and disperse it
into the air.  You can glue one to the top of your cpu.  I believe
there is such a thing as thermal-conductive epoxy, but since I
haven't put a sink on my cpu yet I can't tell you exactly what they
call this stuff, or what type of heat sink to ask for.


Credits
-------
I was far too wimpy to be the first guy in the world to try this.
That distinction goes to <forgot his name> at CalTech and Paul A. in
Australia, who was kind enough to send me his procedure for performing
the upgrade.

Good luck.  May the Quartz be with you!  

--George John




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