randy@cctb.wa.com (Randy Orrison) (06/22/91)
I think I've seen people recently (or maybe not so recently, I haven't
really been keeping up) requesting RAM upgrade instructions for a 1Meg
motherboard. Here's what I've hoarded away on the subject. Maybe
someone could clean this up and archive it on osu-cis or someplace?
-randy
>From: ditto@cbmvax.UUCP (Michael Ditto)
Subject: Re: 1M to 2M revisited...
Message-ID: <4389@cbmvax.UUCP>
Date: 1 Aug 88 19:40:44 GMT
Reply-To: ford@kenobi.cts.com (Michael Ditto)
Organization: Commodore Technology, West Chester, PA
In article <8570002@eecs.nwu.edu> morrison@eecs.nwu.edu (Vance Morrison) writes:
>I have some friendly advice for those interested in upgrading the
>motherboard ram. It is not as easy as plugging in the ram chips.
[ ... lists some other things that are required ... ]
Then, in <574@bacchus.UUCP> darren@bacchus.UUCP (Darren Friedlein) writes:
>I've done all this (4 multiplexers, all the chips, a capacitor on each
>chip, the resitor packs and set the jumpers like I was told (same as
>1M in 4 banks). Still doesn't work. Anyone know what's missing?
I've upgraded a 1Meg 7300 to 2Meg, so I know it's possible. I didn't
have to change the jumpers, since they specify chip size (64K vs. 256K).
I DID have to cut two traces and jumper them somewhere else.
Unfortunately, I didn't write down what the changes were, and I don't
have my hardware manual handy; but they were related to address decoding
and selecting one bank vs. the other. I'll try to get the details and
post them soon.
I feel guilty about posting this teaser ("I've done it, but I'm not
gonna tell you how, nyah nyah" :-) because I did exactly the same thing
about 5 months ago. The thing I was waiting for then was to make the
same mod to a second machine and take careful notes so that I could tell
you all about it. Well, I never got around to it (and no longer have
access to that 7300 or the one I hacked), so I'll have to study the
schematics again and hopefully I'll remember the exact mod; at the least
I should be able to give some pointers.
Good luck, hardware hackers!
--
-=] Ford [=-
. . (In Real Life: Mike Ditto)
. : , ford@kenobi.cts.com
This space under construction, ...!ucsd!elgar!ford
pardon our dust. ditto@cbmvax.commodore.com
>From: pfales@ttrde.UUCP (Peter Fales)
Subject: Successful upgrade of 3B1 from 1MB to 2MB
Message-ID: <810@ttrde.UUCP>
Date: 4 Jan 89 15:42:39 GMT
Organization: AT&T, Skokie, IL
After much trial and tribulation, I finally managed to get my UNIX-PC upgraded
from 1MB to 2MB on the system board. I thought others might be
interested in hearing the procedure.
First, the obligatory warnings: DO NOT ATTEMPT THIS UNLESS YOU ARE
REASONABLY COMPETENT WITH A SOLDERING IRON. This is a major modification
to the board and there is a chance of damaging the board beyond repair.
(Especially with the limited diagnostic tools provided with the PC.) Later,
I will discuss some of the problems I had and how I solved them, but
I hereby disclaim responsibility for anything that might happen to your
system as a result of these procedures.
MATERIALS REQUIRED:
-------------------
36 256KB - 150 nanosecond DRAMS
36 16 pin sockets (optional but recommended)
27 0.1 microfarad bypass capacitors, 0.3 inch lead spacing
4 74F258N multiplexors
4 33 ohm resistor packs (these are 8 pin packages containing four
resistors, each one connected to two adjacent pins inside
the package. You can also use 16 discrete 33 ohm resistors,
that's what I did.)
1 Roll of good quality rosin core solder
1 Grounded tip, fine point, soldering iron
1 "Solder sucker" for removing old solder from the board
1 Stiff bristle brush (e.g. toothbrush) for cleaning solder splashes
PROCEDURE:
----------
1) Use the soldering iron and "solder sucker" to remove the solder
from all the holes where the DRAM sockets, bypass capacitors,
multiplexers, and resistor packs will be installed. I did most
of this work from the top side of the board, without removing
the motherboard. Most of the holes could be de-soldered
easily this way. A few however, particularly the ones connected
to power and ground, may be more stubborn. I just left the
ones that gave me trouble until later when the system board is
removed from the computer.
2) Power up the system and verify that everything still works.
3) Remove the system board from the computer. I discovered after
the fact that this is best done by removing all the screws holding
down the board, as well as the two screws at the sides and the
two screws on the bottom of the metal back plate (the one that
the RS-232 and printer connectors are bolted to.) The metal
back plate should be left fastened to the back end of the system
board.
4) Finish desoldering any holes that were not desoldered in step 1.
This is can done by heating the solder side of the
board, and using your other hand to suck the solder from the
component side of the board, while using your third hand to
hold the system board itself. :-)
5) Install the 36 DRAM sockets in the system board. The only thing
to watch out for here (and in the remaining steps) is that some
of the pins protrude a good distance from the solder side of the
board. When the board is bolted back into place, these pins can
bend and touch something they are not supposed to. (This happened
to me.) If I was going to do this procedure over again, I would
clip all the leads off flush with the board (or bend them flat)
before soldering to keep the sharp points from protruding too far
from the board.
6) Install the 27 bypass capacitors at the appropriate locations,
observing the same precautions as in step 5.
7) Install the four 74F258N multiplexors and the associated resistor
packs at locations 12A, 11B, 11C, and 11D, again observing the
precautions in step five. As previously noted, I had trouble
getting a hold of the resistors packs, so I just used sixteen 33 ohm
resistors and it seems to be working fine.
8) If you are really paranoid, you may want to connect the board
back into the system to verify that it still boots
and runs as a 1 MB system. If not, just plunge ahead.
9) I am aware of two types of motherboards. One is designed for
the 512K system board only, and can be identified by three pins
near 12A labeled E1, E2, and E3. I understand, though I have
not done it, that this board can be upgraded to a 2MB system by
removing all 72 64K DRAMS and replacing them with 256K DRAMS. This
jumper determines whether 64K or 256K DRAMS are being used.
The second type of board can be configured for either 512K, 1MB,
or 2MB. This is what I have. There are two banks of jumpers/resistors
near 12B and 11H. If you have a 1MB system, these should be
configured as follows.
1 MB system:
o--R 145--o 1K resistor o---JR1---o Empty
| |
o---JR5---o Empty o---JR7---o Empty
|
o--R 144--o Empty o---JR8---o Jumper
|
o---JR 6--o Jumper o---JR9---o Empty
|
o--JR10---o Jumper
Converting to the 2MB system involves moving JR10 to JR9, removing
R145, and installing a jumper JR5.
2 MB system:
o--R 145--o Empty o---JR1---o Empty
| |
o---JR5---o Jumper o---JR7---o Empty
|
o--R 144--o Empty o---JR8---o Jumper
|
o---JR 6--o Jumper o---JR9---o Jumper
|
o--JR10---o Empty
10) Install the 36 DRAM chips in their sockets. Make sure that
pin 1 is in the same orientation as the other chips on the board,
and that no pins are bent or broken.
11) Carefully inspect the board for any bent pins, solder bridges,
or unsoldered pins. The toothbrush is handy at this point for
cleaning off dust and solder splashes. A magnifying glass may
be useful as well. Re-solder any suspect connections.
12) Install the system board back in the computer.
13) Boot the diagnostic disk and look for 2MB on the system board.
Run the memory diagnostics, and wait for successful completion.
Congratulations, you have done it!!
DO YOU REALLY WANT TO DO THIS?
------------------------------
After installing the new RAM, there does seem to be a noticeable
improvement in performance, especially in using the User Agent
which is one of the slowest things to begin with. I also noticed
a dramatic improvement in the time required to run "compress"
on large files. Unfortunately, one thing I forgot to do was
run some sample benchmarks on both the old and the new system
in order to get some real numbers to compare. If anyone else does
this upgrade, they may want to run some tests and post their
results. I may do this myself if I get real ambitious, but I
have a lot of other things to do first.
THE WARNINGS AGAIN:
-------------------
THIS PROCEDURE HAS WORKED SUCCESSFULLY ONCE, BUT COULD BE HAZARDOUS
TO THE HEALTH OF YOUR SYSTEM BOARD. I CAN TAKE NO RESPONSIBILITY
FOR ANYTHING THAT MIGHT HAPPEN TO YOUR SYSTEM OR ITS
PERIPHERALS.
----------------------------------------------------------------------------
The following sections should be of little interest to most people, but
are included to describe some of the debugging problems I had.
----------------------------------------------------------------------------
IN CASE OF TROUBLE:
-------------------
If you are like me, things will not go this smoothly. When I
had carefully done everything listed above and turned on the
computer, it just sat there with a blank screen looking at me.
Oh S--t.
The following is not intended to be an exhaustive guide to
trouble-shooting a 7300, but gives some tricks I found that made
it possible to debug my system.
If you turn on the system, and nothing appears on the screen, look
at the LEDs in the corner of the system board. If two of them are on
it means that the built-in memory diagnostic has failed, and there
is still hope. If you see some other pattern, some other damage
has occurred to the system and you are on your own as far as getting
it repaired or replaced.
First, put the jumpers back in the 1 MB configuration and boot
the system. If this does not work the problem is either with the
original RAM or the data lines common to both banks and should narrow
the problem down a bit.
A data sheet for the 256K DRAMS is probably handy at this point.
The memory on the board is divided into 4 banks of 18 chips
each. These banks are selected using the RAS lines on the
DRAMS. You can verify this with a continuity tester, noting that
all the RAS lines in each of the four rows of two chips are connected
together. Banks 3 and 2 are the original DRAMS, while banks 1
and 0 are the newly installed devices.
The jumpers at 11H control the RAS decoding and are wired like this:
-----------------
+5 Volts o--R 145--o----| A1 |
| | |----- RAS3
LA2 o---JR5---o | |
| |----- RAS2
+5 Volts o--R 144--o----| A0 |
| | |----- RAS1
LA1 o---JR6---o | |
| |----- RAS0
| Decoder |
-----------------
In the 2MB configuration, address lines 2 and 1 are used
to select one of the four RAS lines. In the 1MB configuration
only LA1 is used, and A1 is pulled high. This ensures that
only RAS3 and RAS2 will ever be selected.
By looking at the figure above, you can see how it would be
possible to move the jumpers to connect the 5 volt pullup to A0,
and LA1 to A1. This will still be a 1MB configuration, but uses
RAS3 and RAS1. In other words, it uses 18 of the original DRAMS and
18 of the new DRAMS. Try booting the system in this configuration.
You should also be able to see from the above figure how to
connect LA1 to A1, and Ground to A0. This will select only
RAS2 and RAS0, in other words the other half of the original
RAMS and the other half of the new RAMs. Try booting the system
in this configuration.
If you are lucky, one of these configurations will boot, and
one won't. This will narrow the problem down to one bank of
devices. Some careful work with a continuity tester should
isolate the open or shorted connection. You may also want
to try swapping the upper and lower banks of the new DRAM to
determine whether the problem follows the devices or the
sockets. (Aren't you glad you used sockets?)
This was how I found the problem on my board. It turns out
that one of the address lines was shorted to ground, pin 1 of
one chip had bent over and come in contact with pin 16 of the
chip next to it which is ground. Once I fixed this, the system
worked beautifully.
--
Peter Fales AT&T, Room 2F-217
200 Park Plaza
UUCP: ...att!ttrde!pfales Naperville, IL 60566
Domain: pfales@ttrde.att.com work: (312) 416-5357
>From: mvadh@cbnews.ATT.COM (andrew.d.hay)
Subject: Re: Successful upgrade of 3B1 from 1MB to 2MB
Message-ID: <2981@cbnews.ATT.COM>
Date: 10 Jan 89 13:19:08 GMT
Organization: AT&T Bell Laboratories
In article <810@ttrde.UUCP> pfales@ttrde.UUCP (Peter Fales) writes:
>After much trial and tribulation, I finally managed to get my UNIX-PC upgraded
>from 1MB to 2MB on the system board. I thought others might be
>interested in hearing the procedure.
thanks very much, peter. a second Mb had been languishing in my
machine unutilized, because i couldn't figure out how to access it.
however, i had to do quite a bit of detective work myself.
my motherboard isn't like peter's: it has no jumpers above JR4 and no
r145. furthermore the schematics (fortunately [?] i have the tech.
reference manual) are inconsistent, and even inaccurate!
they show the 1Mb board as having JR6 and JR10 -- which mine doesn't
have -- and the 2Mb board doesn't have any of these jumpers, but shows
the same signal configuration as the 1Mb board!
on my board, 25f pin 15 was lifted, and jumpered over to 13b pin 11.
6j pin 3 was jumpered to 6k pin 1. jr1 was in the e1-e2 position.
by scrutinizing all 3 schematic sets (.5M, 1M, & 2M), i deduced that
these corresponded to jr10, r145 (6k:1 is pulled up), and jr8.
25f:15 is la2, so it was obvious that i had to remove the 6j:3 - 6k:1
jumper and re-establish 25f:13 - 6j:3. a continuity check showed that
the pad under 25f:15 still went to 6j:3, so i hooked it to its pin
with a short piece of wire-wrap wire, soldered.
i tried booting. my system still showed 1Mb. what was wrong?
where i hadn't followed peter's instructions, my board mached the 2Mb
schematics. scrutinize the schematics again...
the .5M set showed 13b:11 (and 13b:2,5,14) going to ma20 instead of
la2. my first mod was basically removing a factory hack; was this one
too? ma20 is available on 25f:8, so i pulled the long jumper off
25f:15 and tacked it to 25f:8. bingo!! 2Mb on bootup!
so i cast around for a neat way to make it permanent. ma20 also goes
to 19c:14, which is right alongside the jumper, so i cut the jumper
about 1.5" long, strip the end, and solder it to 19c:14.
it still works!
now i go on to bigger and better things...
--
Andrew Hay +------------------------------------------------------+
Apprentice Polymath | Yes, the wages of sin ARE death, but after they take |
AT&T-BL Ward Hill MA | taxes out, it's kind of a tired feeling really |
mvuxq.att.com!adh +------------------------------------------------------+
--
Randy Orrison Chemical Computer Thinking Battery
uunet!microsoft!cctb!randy randy@cctb.wa.com
"Paradise is exactly like where you are right now,
only much, much, better."