Modifying Memory Modules - Reports

Mod reports from various sources.

A very happy IBM L40 SX (4 MB)
N51SX(8551) (2 MB)
Make ordinary memory look like IBM´s (PS/2 76i, 16 MB)
8 MB PD for PS/2 Note N51sx


A very happy IBM L40 SX (4 MB)
From Peter H. Wendt

Hello! I can't tell you how happy I have been, after being able to convert a 2nd hand generic 4Mb RAM that I bought for 20 US dollars (everything is expensive in Japan but it's considered to be very cheap in this respect...) for my laptop. I don't know what make it is since I bought it from a tatty second hand shop! I only know it operates at 80ns and is produced by Toshiba. I'll try to get some useful info to you tomorrow. Memory banks are on both sides of the chip. Bank 4 (see diagram) is very close to the 0 ohm resistors which are placed directly about pins 69-70. One can see the tracks directly linking pins.

A diagram of the module:

Before conversion:


+------------------------------------------------------------------------+
|                                                                        |
|                                                                        |
|        bank1            bank 2           bank 3          bank4         |
|                                                                        |
+-+                                                           xxox       |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                    Round notch about 2mm deep

o= open connection
x= zero ohm resistor


After conversion:


+------------------------------------------------------------------------+
|                                                                        |
|                                                                        |
|        bank1            bank 2           bank 3          bank4         |
|                                                                        |
+-+                                                           ooxx       |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                    Round notch about 2mm deep

I removed the notch on my computer and slotted the chip in. No problem apart from getting a 164 error message.
A very happy man indeed!

Now......my next project is to find a cheap hard disk suitable for my little machine. Can you give me some idea....there are 2.5 mm IBM hard disks available for PS/2 55. I wonder how to convert them, if possible.

Best regards from Japan

William


N51SX(8551) (2 MB)
From Billy Wiggins

Peter,

I would be happy for you to add it to your site. All I did was use a standard 72 pin 2MB 512K x 36 PNY SIMM and add the jumpers to it and wound up with the gnd on 68 and 70. I also clipped the plastic tab on SIMM socket. (Like that was gonna stop a true hacker)

I don't think I could make up a schematic with my mailer. What's your pages address I would like to see it.

Billy
Albany, Ga


So - while just being busy on reworking my pages, I tried to picture Billys modification on the 2MB-module. It will probably be not exactly how his module looks like - but show the principle.

A diagram of the module:

Before conversion:


+------------------------------------------------------------------------+
| ################  ################  ################  ################ |
| ##### Bank #####  ##### Bank #####  ##### Bank #####  ##### Bank ##### |
| ####### 1 ######  ####### 2 ######  ####### 3 ######  ####### 4 ###### |
| ################  ################  ################  ################ |
+-+                                                           xxoo       |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                     ^--Round notch about 2mm deep

                                                              ||||
o= open connection                                         67-++++-70
x= zero ohm resistor                                           ||
                                                           68--++--69


After conversion:


+------------------------------------------------------------------------+
| ################  ################  ################  ################ |
| ##### Bank #####  ##### Bank #####  ##### Bank #####  ##### Bank ##### |
| ####### 1 ######  ####### 2 ######  ####### 3 ######  ####### 4 ###### |
| ################  ################  ################  ################ |
+-+                                                           oxox       |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                     ^--Round notch about 2mm deep

o= open connection
x= zero ohm resistor

In case Billy manages to rework a 4MB- or 8MB-module, the results will be published here as well.


Make ordinary memory look like IBM´s (PS/2 76i, 16 MB)
From Morten Kristensen

Hi,

I have a ps/2-76i. A few months ago I realized that I needed more memory. So I asked around for 2 pcs. IBM 16MB parity modules. But they were way to expensive for me, so I took a chance and bought two ordinary Texas Inst. 16Mb 60ns true parity sims. Of course they didn't work, but then I remembered seeing the scheme of how PS/2 identify sim-memory (on one of your pages) pin 67,68,69,70.

I then soldered pin 67 and 70 *) to ground (pin72) (making it a 16MB 70ns parity) and viola I had two IBM compatible parity modules, for less than half the price! It have been working perfectly for two weeks now running Win95.

It might work with other machines/modules !!??

Hope you can use this on your webpages.

--
Morten Kristensen; mailto:morten@unidhp1.uni-c.dk
Phone +45 xxxxxxxx Mobil +45 xxxxxxxx

*) I think he made a mistake here: 16MB/70ns Parity is 67+69 tied to 72 (Peter)


8 MB PD for PS/2 Note N51sx
From Jim Shorney

Paging Mr. Wendt!

Thank you again for your wonderful page on IBM presence detection for memory modules. I acquired a new toy last night, an 8551 N51sx notebook (traded one of my model 80's for it). I've been playing with it and decided it was badly in need of more RAM, so I went to your page and did some studying.

After a few minutes of tinkering, I was able to determine that the PD code for an 8 MB Parity SIMM in this beast matches the configuration for 8 MB non-parity on your page (which is marked "reserved" in the parity RAM chart). That is, pin 70 shorted, all others open. I also determined that the machine does definitly require parity memory, but the industry standard 8 MB parity module works fine and passes diags. Had to trim that white nub on the socket down for it to seat properly, of course.

The N51sx also seems to be an IML machine, FWIW.


Now if I can just find a bigger SCSI drive for it... Has anyone had any luck using IBM OEM drives from Apple Powerbooks in x86 machines? I have one here, but have never gotten it to work properly in anything but a Powerbook, and it does seem to have an Apple ROM in it.


Jim

--
Jim Shorney
jshorney@inebraska.com
Lincoln, NE, USA
http://incolor.inetnebr.com/jshorney


I try to bring a diagram of the module, how it probably looked like:

8MB / 70ns - Before conversion:


+------------------------------------------------------------------------+
| ################  ################  ################  ################ |
| ##### Bank #####  ##### Bank #####  ##### Bank #####  ##### Bank ##### |
| ####### 1 ######  ####### 2 ######  ####### 3 ######  ####### 4 ###### |
| ################  ################  ################  ################ |
+-+                                                           ooxo       |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                     ^--Round notch about 2mm deep

                                                              ||||
o= open connection                                         67-++++-70
x= zero ohm resistor                                           ||
                                                           68--++--69


8MB / 80ns (N51) - After conversion:


+------------------------------------------------------------------------+
| ################  ################  ################  ################ |
| ##### Bank #####  ##### Bank #####  ##### Bank #####  ##### Bank ##### |
| ####### 1 ######  ####### 2 ######  ####### 3 ######  ####### 4 ###### |
| ################  ################  ################  ################ |
+-+                                                           ooox       |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                     ^--Round notch about 2mm deep

o= open connection
x= zero ohm resistor



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