More RAM for my 7300
Norman Yarvin
yarvin-norman at cs.yale.edu
Sun Sep 9 12:44:43 AEST 1990
calvin!mark at ncoast.ORG (Mark A. Fleming) writes:
> An excellent step-by-step description of the process was posted about
>two years ago.
I saved three long articles; here they are. I saved these for my own use;
there are no attributions included. I believe credit for the first goes to
Craig Votava; I'm not sure about the other two. Perhaps the last is due to
Thad Floryan? In any case:
---------------------------------------------------------#1
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..."
--------------------------------------------------#2
With all the curiosity about expanding the .5M on DDD's el-cheapo UNIX-PCs,
I figured that it was about time to rummage though my archives for this old
gem that was passed along to me by Gary Sanders (gws at n8emr). Of course,
ordering another UNIX-PC from DDS has kept needling me to find this stuff.
I cannot vouch for the '>'ed instructions, as my current UNIX-PC is a 3B1
that already had 2M on it. I don't expect to expand the RAM on the
stripped system I just ordered until chip prices fall.
<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.
I bought two more of these used tools last Saturday at the Dayton Hamvention.
If you have trouble finding some yourself, I can stand to part with them for
ten bucks each.
< 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.
Get only "machine screw, high reliability" sockets. Yes, they do cost a
bundle, but are worth every penny. Notice that the few sockets on a UNIX-PC
motherboard are this good style. Make sure that the sphincter is gold plated.
It is nice to have gold plated leads, but not necessary.
< 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??
Aside from the commercial flux stripper solutions, I've found the best thing
to be a two step process: First use acetone. It strips the actual rosin
damn fast, but leaves a power residue where the flux actually have to do
work on some oxide. Second, use a heavy Freon solvent such as TF. It does
an excellent job of dissolving the powder.
The acetone is nasty powerful stuff. Don't come in contact with it. If
you can smell it at *all*, that's too much. I always set up a window fan
do suck away the vapors.
Many people use Freon alone. It *does* work, but Freon alone is very slow
at stripping the bulk of the rosin.
< 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!
I often use Q-tips to both apply the acetone and remove the crud. Roll it
over the board. This creates much less vapor than spraying or pouring
acetone over the board. It also eliminates the need for having something
to catch the excess solvent.
< 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!
-------------------------------------------------#3
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.
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