Tutorial: 200LX memory upgrade

Archived 2013-12-08
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Another memory upgrade

See also: Tutorial: Disassembly of a 200LX 

This article has been written by Carlos Izzo Videla, Buenos Aires, Argentinia. He asked me to host this valuable piece of information here on www.hermocom.com.


After going round in circles for a while, I finally found a viable and inexpensive alternative to the different commercial memory upgrades for the HP200LX that are available on the web. In a relatively short time and with a limited investment, I was able to add 4Mb to my stock (SG-June '86) 2Mb palmtop by "piggybacking" two 2Mb memory chips atop the on-board memory chip.


I do not advise anyone doing this nor do I endorse this procedure in any way. If you are not naturally curious and don't have a strong knack for and experience in opening up things even if only to see what's inside and try to learn how they work, please heed my advice: do yourself a favour and stop reading this right now. In carrying out this procedure, you'd be opening up and practising major surgery on your precious HP200LX palmtop in a way that would absolutely void the warranty on any PDA, HPC, electronic or electrical appliance and running a very high risk of causing irreparable damage to it.

All the information I have put forth in this screed is freely available on the web: by NO means and under NO circumstances will I accept ANY responsibility for ANY damage to anything or anyone that carrying out this modification to your HP200LX could eventually cause.

"THE DEVIL MADE ME DO IT" (Flip Wilson's Geraldine in Rowan and Martin's "Laugh-In" - 1969)

I've been naturally prone to folly and risk from a very early age as well as overly confident in my manual dexterity. This is probably the reason why I saw no impediment in exploring the possibilities that this 'do it yourself' memory upgrade could open for me and thus decided to go ahead with it. It's also quite possible that the Gods were smiling upon me that particular day or that it has been a fluke of sorts that I didn't toast my HP200LX.

It is at this point that I'll insist once again: there is more than one purveyor of memory upgrades for the HP200LX on the web and I'm quite sure sure any one of them can do a good job in a cost effective manner and without any risk to your HP200LX palmtop.

In short: if not for the Gods' fickle humour or a fluke, you are on your very own.


When I purchased my 2Mb HP200LX, the first thing I did (after taking it apart, of course) was to search the web for the different hardware hacks that could eventually be applied to it. A memory upgrade and a DS modification seemed to be the most important ones, but my unit's configuration had only one 2Mb chip, no empty places to fill on the motherboard, no expansion board, not even the memory expansion connector. So after installing a 32Mhz crystal, I went on to look for a viable memory upgrade solution.

This post (broken link, will be updated once the HPLX-L archives are available again) to the HPLX list by Michel Bel (04/03/2002) and subsequent follow-ups by others gave me an idea for expanding the memory of my HP200LX. The critical information I needed to make this memory expansion idea a reality arrived in the form of a very interesting and well written page posted here (broken link!) by a fellow by the name of Rudy Moore to whom I would like to express my gratitude.

Thank you for sharing your work, Rudy!

Please note that I consider Moore's article to be mandatory reading for anyone who is considering running the risk of going ahead and attempting this memory upgrade.


As you have surely grasped, Moore's careful and well documented approach does not use the "piggyback" method I am using here. IMHO, this one is more convenient (albeit more technically challenging) as it allows for the use of two chips without the resulting wire clutter that would otherwise be generated in the very limited space available under the HP200LX's motherboard.

Nevertheless, it does have a couple of drawbacks:

1. You have to get your hands on a specific chip type (1Mx16 1K refresh 3.3v EDO DRAM) and it's not too easy to find. You either pull it from unused older equipment or purchase it from whoever has it in stock. I have seen them with asking prices ranging from US$15.00 to US$25.00 apiece (much too dear, I think). In this case, I used a pair of Toshiba TC51V18160AFTS-70 chips that I unsoldered from a T1910's 8Mb memory card. This chip is, AFIK, identical to / compatible with this Micron chip which in turn is identical to / compatible with the on-board chip my HP200LX has.

2. The chips have to be soldered directly on top of the existing one (hence this technique's name), which is not an easy task to carry out. A stable pulse and sharp eyesight as well as very good soldering skills are a must.

3. One memory chip on top of another and so on could, in theory, impede proper dissipation and acumulate heat. I don't think that a DS HP200LX could cause the three piggybacked chips to overheat, but I really don't know for sure.

I won't make any of the obvious recommendations (ESD protection, back-ups, etc.) for I think that anyone who is up to doing this you should know what to do. I won't delve into the gory details of how to dismantle a HP200LX either: it has already been thoroughly documented by two very experienced LXers: Daniel Hertrich has done it here and David Sargeant has done it here.

With Moore's general procedure and instructions as a guide plus the Micron data sheet (thank you for the tip, Mack Baggette!!!) for the chips I had, I set out to map out and verify the on-board chip-to-memory connector pinout. Once I checked and double checked that the pinout was correctly mapped out, I drew up the wiring diagram shown below:

Wiring Diagram

I have used electronic soldering equipment a myriad of times but never acquired the sort of soldering skills this job requires. The use of the right soldering wire, paste, wick, proper size tips and temperature are of prime importance so if you lack the specific knowledge involved or your pulse and eyesight are as challenged as mine, please think it over and have someone fit and knowledgeable perform this task for you. I may be prone to folly and risk but not dumb: off I went to see my good friend César Viglianco at his downtown electronics lab. He once performed an AMD5x86 SMD chip transplant into an ageing 486DX laptop for me and this job was a walk in the park for him.


Once you've dismantled the palmtop and carefully taken out the motherboard, turn it over and secure it adequately on a stable working surface. Here's a photo of the motherboard showing the on-board memory chip and the memory expansion connector pads:

On-board chip

The memory chips used must be carefully examined with a loupe to make sure that there's no extra plastic along the borders (very carefully shave them off with a sharp x-acto type blade) that could keep them from fitting perfectly in place and in full contact with the one below. After that, all the chip's pins (with the sole exception of the RAS# pin) must be bent downwards so that once it is in place they come into contact (even if very lightly) with the pins of the chip below it. Work slowly and be very careful when you do this !!!

If all this is done properly, once the soldering is finished the electrical continuity between the chips will have been assured, the limited space available underneath the motherboard won't be compromised and you'll have no problems when it's time to assemble the palmtop again. Like in any similar situation, be sure to check and double check everything before deciding that it's OK to go ahead and use the soldering pencil on your palmtop's motherboard. Patience and Prudence will be your very best girlfriends when doing this. If necessary, stop, go have a beer with them and return to the worktable afterwards.

The critical part of this upgrade job comprises a two step process which basically involves stacking two additional memory chips on top of the existing on-board memory chip, wiring up their RAS# pins to the RAS1_ and RAS2_ pads on the motherboard, closing up and then checking to see that everything works properly.

In the first step, one of the memory chips is soldered on top of the existing on-board chip and it's RAS# pin is wired to the RAS1_ pad on the motherboard.

Here's a photo showing the result:

First additional chip in place

Closing up the HP200LX, checking to see that everything works properly and that the system reports an additional 2Mb clears the way to the next step.

In the second step, the other memory chip is soldered on top of the first one and it's RAS# pin is wired to the RAS2_ pad on the motherboard.

Here's a photo showing the result:

Second additional chip in place

Here's another photo (not too good, I'm afraid) showing the finished job from another angle: two 2Mb chips soldered on top of the original on-board memory and with their RAS# pins wired to the corresponding RAS1_ and RAS2_ pads on the motherboard.

Lateral view of the three piggybacked chips

The memory upgrade is finished when you close up the HP200LX, check to see that everything works properly and make sure that the system reports a total of 6Mb available memory, as shown in this screen capture below:

6mb Screen shot

That's all there is to it ... ;-D

Interesting links related to this page:

Rudy Moore's site.
David Sargeant's page.
Micron data sheet.


Copyright © 2008-2010 Carlos Izzo Videla. All rights reserved.
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