Modifying Memory Modules


Warning: This is neither a joke nor is it intended for Beginners or Wanna-Bees. All Tips given and all the described modifications are "On Your Own Risk". Author takes no responsibility for any damage whatsoever resulting from the use of information on this site! Read the entire article first, before you begin. Good luck!

Picture this, you've got

  • PS/2 Laptop L40SX (8543)
  • N33SX-G15 (8533) but not -G13!
  • ThinkPad TP350 (2618)
  • ThinkPad TP710T (2523)
    (If you don't know what this is: Look under "PDAs and other Dead-Ends"!)
  • N51SX / N51SLC (8551)
First Look: Is it working? (Assumed it is.)
Next Look: How much memory has this thing? Uh - only 4MB? Or even less? 2MB?
Yeah, that's not enough, let's upgrade the thing! Quick look into the parts list for 40SX... Aaaah! They want WHAT?! For only 4 MB RAM?! That's robbery!

Sure it is. Why? Because IBM had made some special, unique modules for these machines, like they often used to do. They say it were 'Low Power Modules'... hmm. One can believe it, or not.

Eh, at least the modules have different part-numbers than anything else.

4 MB / 80nS Parity ModuleP/N 79F1000FRU 79F1003
8 MB / 80nS Parity ModuleP/N 79F1001FRU 79F1004

But still...


Here's a way to fake them out !
At least on the 4MB part

The known facts:

First: the module connector on the above mentioned machines is different in the way that the module doesn't stand upright or in a 45-degrees angle, but is laid horizontal (parallel to the systemboard).

Second: the above mentioned modules differ from others by the fact, that the notch in the middle between the connector pins is deeper - about 4 mm instead of 2 mm on other modules.

Third: the modules need a particular "Presence Detection" coding to be properly recognized.

And not to forget: the access-speed of them is 80 NanoSeconds (nS).

What to do ?
Easy: At first get a 4MB/70nS module for the PS/2 or PS/VP-series. There are a lot on the market and I'm pretty sure that the modification will work on many of them.

Some people asked:
"Why a 70nS module, if the L40 uses only 80nS modules ?"
Two reasons.
First: 4MB/80nS Parity modules are not that easy to get.
Second: a module with 70nS-specification run at only 80nS-requirements will have a lower power consumption than one built for 80nS.

Attention: The module height -from connector row to the top- may not exceed 1 Inch (25.4 Millimeter). Higher modules will not always fit into the systems.

I tried two modules: IBM P/N 71F7010 (FRU 92F0105) and IBM P/N 68X6343. They're IBM, because I have a faster access to IBM parts than on any 2nd-source part. I'm confident, that the principle will work on modules from other brands too.
Unless: I haven't tried it. Report your experiences !

Well - it's easy doing with this IBM-module. The 71F7010 has a label with "4MB70NS OS/2" on it and has 8 chips (514400 / data-bits) on the one side and 4 chips (511000 / parity-bits) on the other.
This kind of module is fairly common and wide spread. It is originally from Hitachi.
The module has -in addition- 3 little 'squares' on the 8-chips-side. A fourth 'square' is printed on the board but unpopulated. These 4 'squares' are connected with one side to the pins 67 to 70 of the module and with 'Ground' on the other side. So the pins are either tied to ground (logical '0') or connected with nothing, which result in a logical '1' for this pin.
Ground is on Pin 72 of the module (see: Diagram further below)

On our module the pattern is the following:

Pin 70 Ground = 0
Pin 69 open = 1
Pin 68 Ground = 0
Pin 67 Ground = 0

Pretty easy to check with a Multimeter in Ohm-Range.

But we need a different pattern for our machines:

Pin 70 Ground = 0
Pin 69 Ground = 0
Pin 68 open = 1
Pin 67 open = 1

"Yeah - that's easy !" ... so let's fire on the solder iron and here we go. Remove the two Zero-Ohm-resistors (sounds more likely than 'bridges') from the one side and connect the one missing on the right side with a piece of tin. Takes about ... 60 seconds or so.

Now, of course you will have to obey the rules for handling ESD-sensitive devices, and of course you will make sure that your soldering equipment is free from mains potential, so that the memory modules won't get destroyed.

Next thing to do is a little mechanic: we have to make the module fit into the memory connector.

I would recommend that it were better to modify the machine, so every module will fit in there. It's sometimes easier by the way.

Simply take a sharp cutter and cut away half of the little plastic 'nose' inside the module connector. Watch the antistatic rules again !

Assumed -by what reason- that you cannot cut away the piece of plastic you will have to use a small file to enlarge the notch in the module. On this particular module it is pretty easy and bears no risks - there are no further connections in this area around the notch. If the notch will have the height of the connecting areas that will do.

Now check out the module. Least thing you will get is a 164-Error (Memory Size Changed) and you will need your Setup-/Reference Disk to adjust the memory size. On the TP710T you will get the new memory size plus the 164, then a reboot and the memory size alone followed by IPL, if everything went right.

That was it !

The rework of the 68X6343-module is basically the same as on the 71F7010 (and supposed to be the same on other '92F0105-compatibles'). But this module is a single-sided module, the memory chips are closer to each other, the bridges are 50 percent smaller and there are some connections close to the bottom notch.
If you can get only one of those modules, I would strongly recommend a modification of the memory connector rather than enlarging the notch any deeper.

A schematic diagram of this module and its modification is given further below too.


Schematic Diagrams
Yes - Peter loves ASCII !


   P68-                                                            P69-
   P67-                                                            P70-
    |                                                               |
    V                                                               V
+------------------------------------------------------------------------+
|   [=]   #####  #####  #####  #####  #####  #####  #####  #####   [ ]   |
|   [=]   #####  #####  #####  #####  #####  #####  #####  #####   [=]   |
|         #####  #####  #####  #####  #####  #####  #####  #####         |
|         #####  #####  #####  #####  #####  #####  #####  #####         |
|         #####  #####  #####  #####  #####  #####  #####  #####         |
+-+                                                                      |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +-- -----------------------------+  +---------------------------------+
                                    ^ Notch about 2mm deep

              (Fig. 1 : Module 71F7010 before modification)


+------------------------------------------------------------------------+
|   [ ]   #####  #####  #####  #####  #####  #####  #####  #####   [=]   |
|   [ ]   #####  #####  #####  #####  #####  #####  #####  #####   [=]   |
|         #####  #####  #####  #####  #####  #####  #####  #####         |
|         #####  #####  #####  #####  #####  #####  #####  #####         |
|         #####  #####  #####  #####  #####  #####  #####  #####         |
+-+                                 __                                   |
  |1 ||||||||||||||||||||||||||||| |  | ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                    ^ Notch about 4mm deep

              (Fig. 2 : Module 71F7010 *after* modification)



+------------------------------------------------------------------------+
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|            ##### ##### ##### #####  ##### ##### ##### ##### X          |
+-+                                                           X  X  X    |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                    ^ Notch about 2mm deep      ^
                                                                |
              (Fig. 3 : Module 68X6343 before modification      |
             The 4 bridges on the module are marked with 'X')   |
                                                                |
                                                             67
                                                             68 69 70

+------------------------------------------------------------------------+
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|##### ##### ##### ##### ##### #####  ##### ##### ##### ##### ##### #####|
|            ##### ##### ##### #####  ##### ##### ##### ##### O          |
+-+                                                           O  X  X    |
  |1 |||||||||||||||||||||||||||||  __  ||||||||||||||||||||||||||||  72 |
  +--------------------------------+  +----------------------------------+
                                    ^ better leave Notch as it is

              (Fig. 4 : Module 68X6343 *after* modification
                   Removed bridges are marked with 'O')


Other Modifications:
  • Successful modification done by William Cheung is described here
  • 2MB-Modification for a N51SX done by Billy Wiggins is described here
  • 8MB Modification for a N51SX done by Jim Shorney is described here
  • 16MB-Modification for PS/2 76i done by Morten Kristensen described here
  • Modification for cheap generic 8, 16 and 32MB modules to make them compatible with PS/2 systems here


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