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Date: Thursday, 30 March 1989  21:12-MST
From: ralphc@tekcae.CAX.TEK.COM (Ralph Carpenter)
Subject: Upgrading PC-AT with 80386 motherboard.
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I have just finished upgrading two 80286 based AT Clones to 80386- 20mhz
systems.  I'll be doing a third one in a week or so.  Only the
motherboards were changed, although we are now considering swapping out
our 1:3 interleave for faster 1:1 hard disk controllers.  Everything has
gone very well, it took a screwdriver and 30 minutes (I watched it done
once before) per system.  See notes below for a description.  No hassles,
really, the hardest part was deciding what and where to buy.
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We settled on a Mylex MI386-20 board with 64k static cache ($1225), and
4mb SIMM memory ($870).  Steve Gibson, the InfoWorld columnist, gave Mylex
motherboards a great review a few months ago.  Not the cheapest board, but
a high quality American made unit for little more than the cheapest
boards, which aren't cache designs.  The board supplier's memory price was
so good (price and availability better than the memory chip manufacturer
would give me) that we upgraded to 8mb.
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Tektronix is almost within shouting distance of a Mylex supplier,
(MicroSource Distributors) so we got an evaluation unit to test for
function and compatibility.  I tried Compaq DOS 3.2, MS-DOS 4.01, IBM OS/2
Extended Edition version 1.1, and OS/2 Sidekick without a glitch.  The
EMM386 driver that comes with DOS 4.01 turned the extended memory into
expanded just as I had hoped.  All my current DOS based applications,
including some finicky ones, seem to work very well.  While some of you
may have access to more extensive software test libraries, I don't.  But,
after reading some reviews of other clone boards, I was pleased to see
OS/2 EE work.  The BIOS is quite full featured and does nice things. I've
never seen a BIOS give me the option to test the hard disk for the optimum
interleave and then format it like this one does.
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The reason I am posting this review is simply to pass along the results of
lots of reading, phone calls to manufacturers and suppliers, and how easy
it was to change motherboards.  I have no connection with MicroSource,
other than as a satisfied customer.  Mylex motherboards are available from
several sources that advertise in the computer trade magazines, but if you
are interested (and to save me from responding individually), my
supplier's phone is 503+645-1490.  They also have an 800 number you can
get from 800 information.
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Swapping an AT mother board may not always be this easy, but here's what I
had to do: (Make note = written notes w/ picture)
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1) Using the setup program for my computer, I found out what NUMBER my
hard drive type is.  This is a number between 1 and 47 or so that tells
the BIOS how many heads and cylinders the hard drive has.  The new
motherboard won't know, and NOTHING WORKS if I couldn't tell it what the
drive type is.
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2) I Disconnected all external cabling from the back of the box: power,
keyboard, printer, etc.
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3) After all the touching of the metal case, I was discharged of any
static charges already, but FORGETTING to discharge myself again after
shuffling in and out of the area before finishing the job wouldn't have
been wise.
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4) I opened the case - 5 screws.
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5) I took out the screws holding the video, etc. cards in place.  Removed
the cards from their slots in the motherboard.  I DID NOT remove any
ribbon cables from these cards unless I carefully made note of the
position and orientation of the cables.  I didn't have to undo ANY cables
to unplug the cards.
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6) I made note of the position and orientation of the two power supply
cables.  Unplugged them from the motherboard.
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7) I made note of the speaker and disk light connector wires, then
unplugged them from the motherboard and hard disk controller board.
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8) I undid the two screws that held down the old motherboard.
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9) The motherboard was now free, so I *gently* slid it out.
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10)There were some white plastic spacers that plugged into holes in the
motherboard that had to be moved to the equivalent holes in the 386 board.
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11)I put the new board in where the old one was.
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12)I put everything back in place, except for the case.
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13)I powered it up, used the built in setup program to tell the BIOS what
hard drive type was.
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14) That's it. Everything ran for me.  I put the case on.  Norton SI = 23.
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NOTE:  This is for information only.  Your mileage may vary, etc.
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			Ralph Carpenter
			ralphc@tekcae.CAX.TEK.COM
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2nd Disclaimer:  Nothing in this posting implies that TEKTRONIX endorses
		 my opinions.
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