0.5M - 2.0M expansion memory upgrade REPOST

[Craig Votava]

Here is the first of a number of upgrades that I promised to repost
to the net. I did this during the summer of '87, and have been running
the board almost continuously since then with no problems.

::::::::::::::::::::::::::::
Hi Folks!

Well, after the having my mailbox stuffed with requests (yea!) I decided
I'd better get this out, so here's my story on "How I Changed My Memory
Board From 0.5MB to 2.0MB".

Before I start, let me say that Mark Hillard (gizzmo!mark), who was at
one time, a NASA solder technician, requests that I emphasize
the fact that attempting to de-solder components can cause damage to the
board. Excess heat causes the foil to weaken which makes it very susceptible
to damage. I guess what he's trying to say (and I agree) is DON'T TRY THIS
WITHOUT HAVING DE-SOLDERING EXPERIENCE FIRST!! Even if you have experience,
go to Radio Shack (like I did) and buy an experimenters board and practice
soldering and un-soldering a garbage chip (or socket) until you get the
knack back! Remember; the less time the iron spends on the board, the better!

Ok, now for the good stuff...

Equipment:

	PCA D-60-00226-00 REV D Copyright 1984 0.5 Megabyte Memory Board
		The only weird thing about the board is that there is a factory
		cut trace near C32 and a 33 Ohm resistor across it. It looks
		like R8 on the schematics, and since I can't find R8 on the
		board, that's what I think it is. It's off of a clock
		(20MHz ??) from the motherboard.

	Weller TC202 60w Soldering Station
		My girlfriend got this for me for about $100.00 for xmas.
		They are GREAT! If you don't want to get this, there are
		others at lower prices. These have a thermostat in the tip
		to regulate the temp., that's the important part. Try to get
		the pencil tip, all I had was the blunt end tip.

	Silverstat AS196 Soldapult - LS197 tip
		For those of you that have never seen one, it's a long (5")
		tube with a plunger in it like a big syringe. You cock it by
		pushing the syringe all the way in against a powerful spring
		and it locks in place. When you hit the button, the plunger
		jumps back sucking air through the hole in the tip. If you
		have the tip over liquid solder, it sucks it right up!
		I borrowed this (thanks Larry!) but they run about $20.00 I
		think. Get extra tips too, that will help.

	72 Sockets
		I don't remember who made them, but mine had round holes
		instead of pressure clamps. Find a hardware guru and have
		him suggest some to you, that's what I did.

	72 Samsung KM41256-15 6222 "Made in Korea" Memory Chips
		I think the "-15" means 150nS. These work fine, and are among
		the cheapest around.

	1 74F258 Memory Decoder Chip
	1 10 Ohm resistor pack
		You only need these if they were not initially put on your
		board. Check to see if there is a 74F258 chip at location
		2-B and resistor pack at RP4. If not, put them there.
		
	Solder
		Make sure you have enough, I ran out about 1/2 way through.
		Mine was Radio Shack rosin core solder, I like the rosin core
		because it cleans the connections before the solder sets. The
		only bad thing is all the rosin left (see next item).

	Denatured Alcohol
		I have a "squeeze" bottle of this that I use to remove excess
		rosin from my solder connections. It works (fairly) well on
		the rosin while not effecting the green "paint" on the back
		of the circuit board. Any better suggestions out there??

	Old Toothbrush
		What you do is douse the back of the board with the alcohol,
		then brush it off with the toothbrush - it really works!

	Ohm Meter
		To check electrical continuity between points

	Orange Sticks
		These were great! They're a stick of wood about pencil size
		with tapered ends. TV repair guys use them for poking around
		in High Voltage areas. The nicest thing is that if you try to
		force something too hard, the orange stick breaks instead of
		the part! How I used them is described below.

	The Computer Shopper Catalog
		This made a GREAT workspace, it's thick enough to be "cushy",
		but doesn't "give" too much to bend the board; and the size is
		just perfect! I didn't ground myself to anything in particular,
		but I was in my bare feet most of the time on my kitchen 
		linoleum.

	Jewelers Loupe
		I had a 5x one to look at traces when I needed to.

	Light
		LOTS of it!

Following will be a description of how I did my board. Many people say that
it's easier to clip the chips off with small, sharp clippers, then unsolder
each pin individually. I may use this method for the motherboard, but for
the expansion board I didn't, so I don't know which way is easier. My method
was to free each pin on the entire chip and extract it intact, this worked
well, and I still have the chips ... maybe I'll put 'em in my mom's apple!

Things to remember EACH time the iron touches the board:
----------
If you're not sure of something ... ANYTHING (is the iron touching the board
correctly, etc), I mean ANYTHING... STOP and start all over on that pin!
Remember if you screw up once, that could be it!

If the pin is not cleaned out properly, re-solder the pin completely back again,
then start over (I know this sounds dumb, and hard to fight temptation on, but
it's really better that trying to get the last bit out 5 or 6 times!).
----------

I'd also suggest that you do 1 or 2 memory chips by themselves first (taking
out the old memory, putting in the socket, then the memory, then running the
board through diagnostics) just to get into the swing. Once your ready to go
into FULL production, follow these steps:

Step 1: De-solder a row (9) chips. Personally, I prefer holding the iron at a
	45 degree angle on the right and the soldapult at a 45 degree angle to
	the left. I used a count of 4 making sure I saw the solder turn liquid
	during the count, then hitting it with the soldapult. A successfully
	unsoldered pin allows you to see the round foil and the pin sticking
	thru the hole. If it looks clean from the foil side, you're ok.

Step 2: Push each pin back and forth at least once from the foil side with
	the orange stick to loosen it from that side (sometimes leftover rosin
	from the initial solder makes them stick)

Step 3: Rub off any excess solder splashes around each pin with
	the tip of the orange stick. While doing this check for lifted foil,
	missed pins, and any other "bad stuff" you can think of.

Step 4: Turn board over to component side and push each pin of each chip with
	the end of the orange stick to loosen it, you may hear a slight
	"tick" as the pin breaks free.

Step 5: When you're convinced the chip is loose, use the end of the orange
	stick to pry up on end of the chip a bit. Then go to the other side,
	and pry it up a bit. Keep going back and forth until it comes out.

Step 6: ALLWAYS check the leads of the removed chip to see if any foil was
	extracted with it. If so, you're already screwed, but at least you'll
	know where the problem is.

Step 7: Carefully check both sides of where the chip was and make sure
	everything is ok.

Step 8: Install the sockets and solder them down. You all know the "be
	carefull's" of this step.

Step 9: Check both sides again and remove the excess rosin with the alcohol
	and toothbrush.

Step 10: Install the memory chips (make SURE they're seated properly) and run
	 diagnostics.

Once you've replaced all of the memory chips and made sure you have the
address decoder chip (2-B) and resistor pack (RP11), all you need to do
is the jumpering and you're set! If you haven't run diagnostics after each row,
now is the time to do it, just to be sure that 0.5MB of the memory you've
installed works.

Jumpering:

On the board is a set of 3 holes in a box labeled "w4" (lower left about at
chip location 1-K. The two lower holes are grouped together, separated by
a vertical line from the third (upper) hole. If you look at the foil side,
the 2 grouped holes (lower) have foil running between them. Remove this foil
and check it with an ohm meter to be sure there is no connection. Now solder
in a small bit of wire coming out of the middle hole and looped around, into
the isolated (upper) hole. Check your work with an ohm meter just to be sure.
This jumper will disconnect address line 11 from the memory address decoders,
and connect up address line 19 (This part is similar to the mother board
upgrade). At this point you can run diagnostics again. If you do this, you
will be checking a different 0.5MB chunk within the 2MB on the board.

There are 2 more similar sets of holes labeled "w1" and "w2" (upper left near
A-1). Use the same procedure to disconnect the existing holes (foil is on the
component side this time) and jump the middle hole with the isolated hole.
These jumpers ground pins 13 and 18 of the 74F373 chip at 1-A (check it with
your ohm meter if you want, ground foil runs around the board edge)
and, in effect, hardwire the board for slot 1 using up ALL available
expansion memory (even though the machine can take 4MB, only 2MB of it
can be on the expansion bus).

W3 simply pulls up +5 volts on pin 73 of the expansion plug. Convergent
claims it is "unused". I've found no reason to disbelieve them. You don't
have to touch this one.

Testing:

THE BOARD MUST BE PLACED IN EXPANSION SLOT 1 OR IT WILL NOT WORK! Expansion
slot 1 is directly under the power supply, or, the slot on the same side as
the volume control for the speaker, or, the right side if you look at the
machine from the front, or, the left side if you look at the machine from the
back. When you boot up from the diagnostic floppy to run diagnostics, you
should see 2M of memory in the expansion slot. The total memory as reported
by the Administration function from your "office" should be 2560k. Be sure
to run diagnostics on it to make sure everything is correct, and you're all
set!

By this point you will have de-soldered and re-soldered 1152 pins!

The only other cautions that come to mind is always handle the board with
care, I have heard of printed circuit boards cracking and rendering them
useless. If you constantly remind yourself that if you screw up once, you're
done for, and never continue when you have a slight doubt in your head, you
should be fine.

I am willing to help anybody who wants, but if you decide to do this, nobody
can take responsibility for what happens but yourself, so "Lets be careful
out there..."

Good Luck!

Craig Votava
AT&T Bell Labs, Naperville IL
IH 4G-324 312/979-2542