[comp.sys.ibm.pc] Upgrading PC-AT with 80386 motherboard.

ralphc@tekcae.CAX.TEK.COM (Ralph Carpenter) (03/31/89)

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.

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.

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.

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 who 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.


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)

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.
2) I Disconnected all external cabling from the back of the box:
	power, keyboard, printer, etc.
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.
4) I opened the case - 5 screws.
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.
6) I made note of the position and orientation of the two power
	supply cables.  Unplugged them from the motherboard.
7) I made note of the speaker and disk light connector wires, then
	unplugged them from the motherboard and hard disk controller
	board.
8) I undid the two screws that held down the old motherboard.
9) The motherboard was now free, so I *gently* slid it out.
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.
11)I put the new board in where the old one was.
12)I put everything back in place, except for the case.
13)I powered it up, used the built in setup program to tell the
	BIOS what hard drive type was.
14) That's it. Everything ran for me.  I put the case on.  Norton
	SI = 23.


NOTE:  This is for information only.  Your mileage may vary, etc.

			Ralph Carpenter
			ralphc@tekcae.CAX.TEK.COM

2nd Disclaimer:  Nothing in this posting implies that TEKTRONIX endorses
		 my opinions.