UNIXPC Motherboard RAM upgrade, 512K to 1MB or 2MB

[Thad P Floryan]

Lenny forwarded a question to me, and I responded privately.

It seems it's time again to generate interest in upgrading the motherboard
RAM on a UNIXPC, so I've edited out the private portions of my reply and
am posting the following.  Enjoy!

....................

The implication from the message Lenny forwarded to me is that you wish to
upgrade a 512K motherboard to be a 1MB motherboard (because you stated you
had 36 256K DRAMs delivered by Santa! :-)

The "usual" upgrade is to 2MB (72 DRAMs) as long as one is desoldering all
the chips and inserting sockets.  You will, in any case, have to remove 72
of the 64K DRAMs even if you want to install only 36 256K DRAMs.

Before you even begin, please, PLEASE, ask yourself if your have the skills
necessary to remove the existing DRAMs without damaging the motherboard.
Several people in our Users' Group have already destroyed their motherboards
because they DID NOT remove the old chips correctly.  In all cases, the
plated-thru hole "barrels" were lifted, causing separation of the traces in
the INNER layers of the motherboard.  Such damaged motherboards are NOT
repairable.  Replacement motherboards are available from Discovery
Electronics or the AT&T San Leandro (CA) Repair Facility.

If you feel confident about removing the old chips (three methods are described
below in "quick" form), then the parts you need are:

1)  one  74F258   NOTE THE "F"; no substitutions permitted.  This part should
	 cost no more than about 25-50 cents.

2)  72   machined-pin IC sockets.  Augat preferred, and BE SURE they are the
         slim-profile so they can be placed side-by-side on the motherboard;
         one guy bought Augats that were a bit wider and would NOT fit side
         by side on the motherboard.  You SHOULD install all 72 sockets even
         if you're only going to install 36 DRAM chips because you will have
         removed 72 64K DRAMs.  Several other mfrs besides Augat also make
	 machined-pin sockets; these sockets are the ones with the round holes
	 on top with a "quality" look; DO NOT SUBSTITUTE the el cheapo sockets
	 with the metal tab that contacts only part of the IC pins ... the
	 trouble those sockets cause in the long run is just not worth the
	 hassle.  You will be spending approx. 12 hours to do the conversion,
	 so spending a bit more for quality sockets (like the ones ALREADY in
	 in the UNIXPC at other expensive IC locations) is a small price.  You
	 can, if you're adventurous, solder-in the new DRAMs and bypass sockets
	 altogether, but ...  :-)
	 These sockets will have 16 pins to match the 256K DRAMs.

3)  one  small jumper wire, such as you can cut from a 1/4 W resistor end.

Removing old DRAMs:

Method 1:    **PREFERRED**

	Get a desoldering tool such as OK SA-150 Vacuum Desoldering Station.
        These cost around $500-$600.  The time one saves is phenomenal.  Simply
        turn the motherboard upside down, put the tool on each DRAM pin, and
        pull the trigger.  Do this to all 1152 pins.  Each DRAM will simply
	fall out once its last pin is freed (assuming the motherboard is upside
	down!) and will be reusable in other systems.  This method will
	probably take all of about 60-90 minutes depending how fast you can
	position the "gun" on each pin (figure 3-5 seconds per pin).

Method 2:

	Get a SoldaPullit (spring-loaded, hand-operated solder sucker) and a
	good, hot, fine-tip soldering iron.  Cock the SoldaPullit, heat an IC
   	pin, wait 'til the solder melts and place the SoldaPullit quickly on
	the connection and press its trigger and hope all the solder gets
	sucked up.  This procedure can take 15-30 seconds per pin, so figure
	on about 5-6 hours.  Cocking the SoldaPullit will probably rub the
	skin off your hands down to the bone before you're through, so plan
	on spending several short sessions instead of a single all-nighter.
	This procedure also assumes the motherboard is upside down.

Method 3:

	From the TOPSIDE of the motherboard, you can clip each pin from each
	DRAM, toss the non-reusable DRAMs in the garbage, then with tweezers
	and a soldering iron remove each pin one-by-one.  Then with either a
	solder wick (like braided wire) or a SoldaPullit, and a soldering iron,
	clear the solder from each DRAM hole.  Figure 12 hours for this method.

	CAVEAT!  CAUTION!  BEWARE!  VORSICHT!   ACHTUNG!   PTOOIE!   ARRGH!

	If you clip the DRAM pins the "wrong" way, you will destroy your
	motherboard.  Now, the correct way (which I did ONCE, before I bought
	the OK SA-150) is to buy a pair of micro flush-cut diagonal cutting
	pliers (figure $30-$50 for a "proper" pair (and, no, such pliers are
	NOT available at Radio Shack)), you MUST clip the pins right at the
	point they enter the IC package, NOT AT THE POINT WHERE THE PINS GO
	INTO THE MOTHERBOARD.  Even with flush-cutters, it's possible to "pull"
	the pins if you clip at the motherboard, and this will destroy the
	plated-thru holes as several people have already discovered.  Example:

                                       _____ clip IC pin here
			+-----------+ /
	              __|   DRAM    |/__
                     /  |           |   \
                    |   +-----------+    |
	____________|____________________|______________motherboard


Once all the 72 64K DRAMs (and pins if you used the "clip" method) are removed,
insert the sockets into the motherboard and solder them in place.

Look along the edges of your motherboard; you'll see reference designations
as letters along one edge, and numbers along another edge (the front edge has
the numbers).  The DRAMs are in the region 2A to 10H.

Locate position 13B on the motherboard (towards the center front edge).  If
there is NOT a 74F258 IC there, insert one (can be soldered directly into the
motherboard).  "Chances are" the resistor pack needed as pullups will already
be in its location on the motherboard; at least, I've never seen a motherboard
without one.

Now, at position 12A, is a jumper JR1 which is really a board trace between
positions E1 and E3; it needs (for a 256K DRAM motherboard) to be re-jumpered
to connect E1 and E2.  You do this using an Xacto knife and cutting the PC
board trace between E1 and E3 and using a wire jumper to connect E1 to E2.  I
don't recall offhand whether the PC board trace is on the topside or the
underside of the motherboard, but it's there and you may need a magnifying
glass and good illumination to see it through the soldermask (the green junk).

For a professional job, I also HIGHLY RECOMMEND you clip all the protruding
pins from ALL the newly-installed IC sockets flush with the underside of the
motherboard; there are special flush edge-cutting pliers for this kind of
operation.  If you DO do this, be sure to do it outside because all the little
bits and pieces can get all over your table, floor, etc.  And be SURE all the
bits are pieces are blown off (with your breath and hands) before bringing the
motherboard anywhere near your disassembled system; a stray particle can cause
a short-circuit on the motherboard and/or other system components.

Finally, install your DRAMs.  Since you've only 1MB worth, use the back four
rows (the front 4 rows of sockets will be empty until you get some more DRAMs).
Each row has 9 columns' worth of DRAM sockets (one byte + parity).

Reassemble your system, then run the memory tests from the Diagnostics disk
for several hours to be sure all's OK.  If you did all the mods correctly,
everything should be fine.

NOTE: I deliberately detailed only the methods and not the techniques of doing
the mod.  If you don't feel comfortable doing the mods and/or this is your
first experience with soldering irons, I strongly urge you to contract a
service technician to do the work for you.  After seeing several people in the
users' group hose their systems because they weren't methodical and were too
over-eager, I have to urge you to be careful.

The mods as outlined above have worked fine for me.  BUT YOU DO THEM TO YOUR
OWN SYSTEM AT YOUR OWN RISK.  I HAVE CHECKED THE INSTRUCTIONS FOR TYPOS BUT
CANNOT BE HELD RESPONSIBLE FOR ANY ERRORS.

The above paragraph is to cover my ass, legally speaking.  Frankly, the mod
is quite straightforward and shouldn't present any untoward difficulties if
you're not all thumbs.

Thad Floryan [ thad at cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]