HPLX.NET HOW-TO: A Palmtop Adventure (text-only)

The other day I was looking at the screen on my 200LX and it seemed that the border (the plastic piece with the words on it surrounding the screen) seemed to be coming off at a corner. Naturally, being a curious person, I immediately set out to see what was under that plastic piece. So, I took a flat-head screwdriver and pried up the edge. The whole plastic strip came off fairly easily, and there was an interesting sight underneath. The screen had a metal border, and there were four hex-head screws. Somebody on the HPLX mailing list brought up the fact that you could create a "secure" display by removing the polarizing filter from the screen. This would render the display blank unless you were wearing polarizing glasses--so you could see what was on the screen, but the person sitting next to you couldn't. (For a more detailed look at LCD technology, visit this LCD FAQ.) This got me thinking about backlighting. So, I decided to disassemble the 200LX and see what I could see.

DISCLAIMER: I am not responsible if you try this.  There are components that could be very easily damaged if you slip up.  Your warranty from HP will be void if you do this.  Don't do it unless you're willing to risk the death of the palmtop.  That said, it's really not that bad if you know what you're doing.


Figure 1: The palmtop open on a bench. The upper part is the bottom case.

This is a picture of the open 200LX. The bottom half is the underside of the keyboard, and the top half is the bottom part of the case. Confusing? There are actually four layers to this thing: the bottom is basically a plastic shell, which the motherboard, speaker, A/C jack, etc. sit in. The keyboard unit clips down on top of that. The screen itself is mounted inside the top piece, which is another plastic shell. In the above picture, the 200LX is closed, and the bottom half has been flipped up for viewing. The big gold circle is the speaker. To the left of that is the socket that PCMCIA cards clip into. This is mounted on the motherboard, the small green circuit board in the upper left corner. All the basic hardware for the palmtop is contained on that small little board! Amazing. See the big green circuit board in the upper right corner of the motherboard, with the white writing on it? This is the TechRam 4MB upgrade.

There is a lot of interesting stuff to see inside the 200LX. I found it interesting that, small as the 200LX is, the actual motherboard hardware is much smaller. Look at the tiny motherboard! Incredible. Imagine what they could cram in there if they used the whole size? 486, 16-bit sound chip, VGA circuitry...

Anyway, if you want to know how to open the 200LX, here are instructions.

Depending on what you want to do, there are two different ways to open your 200LX. If you want to be upgrading your hardware (such as installing a speed upgrade, or a memory upgrade) or fixing a hardware problem, you'll want to open the case itself. If you're just going to clean the contacts of the screen, or something you can do without decent access to the screen, you can get away with just opening the screen's case. However, if you are working more extensively with the screen, such as replacing it or installing a backlight or something, you'll need to open the case anyway to be able to work with the screen. Therefore, we'll start out with a description of how to open the case.

The first thing you need to do is backup your 200LX. Your internal RAM drive will be initialized after this, because you'll have to remove all the batteries. So get that done, turn off the 200LX, and remove the two AA batteries, and your backup battery. Also take off the battery cover and the IR cover. And don't leave an AC adapter plugged in, either. :)

On the bottom of your 200LX you will have four rubber feet. These pop out if you grab them with a fingernail and pull them out. (Be gentle; you don't want to slice the rubber feet in half with a sharp fingernail.) Under each foot is a hex-head screw. You will either need a good small regular screwdriver to unscrew these, or a .05" hex key. I recommend the hex key, as a screwdriver could conceivably strip the screw.

Turn your 200LX upside down, and leave it that way for the rest of this procedure. Unscrew each of the four screws. Don't lose them! I can't imagine where you would be able to find replacements. Once those are out, you need to run your fingernail through the little slot on the side of the case, all the way around. Start at the left rear corner and go along the back, then go back to that corner and go forward and around the front corner (past the PCMCIA slot release slider) and along the front. The 200LX is held together by plastic pegs that fit into plastic holes on the other side of the case. The two that are the most trouble are on the right side of the front, right under the little slot where the screen latch fits into, and a little bit to the right. I was unable to pop these two pegs out of the holes with my fingernail; I had to insert the cap of a pen in after I had already partially separated the case and twist it. This caused the peg to slide partially out, and after that, a fingernail is sufficient.

Once you've got the bottom of the case off, the motherboard may try to come out with it. That's because the springs in the battery chamber are connected to the motherboard by metal snap-in clips on the motherboard. It can be confusing to put the springs back on the bottom of the case if they come off, so you're better off just to pop them free from the snaps on the motherboard. This is easily done, and don't worry, they snap right back on when you close up the case.

Now, if you've followed these directions, you should be able to separate the bottom of the 200LX completely from the top. The bottom will have the battery springs, two other small springs in the middle, a foil overlay covering most of the interior, and a copper disk (the speaker). The most delicate part is the foil overlay. Be careful about bending it; it's a pain to have to bend it back, especially if it gets caught on something when you're reassembling the case.

Now, the other half of your 200LX has all the good stuff in it. Assuming you're looking at it from the front, the left side of the case will be covered by the motherboard. The right side will be black plastic with lots of white spots. Those spots are, of course, the bottoms of keys. Not much you can say about those, so let's examine the motherboard.

The most delicate part of the motherboard is...well, actually, there are two fairly delicate parts. One is the orange ribbon cable that you can see connecting to the yellow connector in the middle of the board. This is your video data cable. Go ahead and insert your fingernail into the release at the top of the connector and pull it out. Once it snaps out a couple of millimeters you will be able to remove the ribbon cable. Now, by lifting up the motherboard, you can completely remove it from the case. The other delicate part is the AC adapter jack, which is not soldered on or anything. It's only held in place by the case when it's snapped together. It is only connected to the motherboard by two very thin wires which are coiled up in the middle. Be careful; it's not too hard to accidentally rip the wires off the motherboard or the AC adapter jack. If this happens, break out the ol' soldering iron.

You can see the slot for the backup battery on the lower left corner of the board. Above that are the IR light-emitting diodes. These will bend if you're not careful, and you could accidentally end up with them behind the case's plastic when you reassemble your 200LX. So be careful! Above this is the serial port. Again, be careful. Those pins are not indestructible! Above that is the AC adapter jack, which we've already discussed. The lower right corner is taken up by the Hornet chip.

Flipping the motherboard over reveals two things of importance: first, the keyboard connector. This is the little strip of black running through the white in the lower left corner. Looking at the bottom of the keyboard, you can see how these connectors press up against each other and make contact. If your contact is off, don't expect much when you try to type. The second thing of interest is the RAM. Depending on your model of 200LX, you may see (right above the keyboard connector) a couple of chips and nothing else, a couple of chips and a connector to the right of them, or just a green daughterboard. The 1MB 200LX's have only the two chips there. I'm not sure if the connector is there or not. Early 2MB versions (with serial numbers earlier than SG6) have the daughterboard. There is 1MB on the motherboard and 1MB on the daughterboard. The later 2MB units have 2MB on the board and no connector for a daughterboard. If you want to be able to upgrade the RAM, you'll have to solder in the connector (or have someone else do it). I'm not sure exactly when HP changed over to the "put both megs on the motherboard" method of manufacturing 200LX's, but one of mine is an SG533, which means it was manufactured in the 33rd week of 1995, and it still has the 1MB daughterboard. I've heard that some later SG5's have both megs on the motherboard. I know that's the case with ALL SG6's. In any case. If you have had a TechRAM upgrade from Times2Tech, or any other memory upgrade, you will see the daughtercard in the connector. The daughterboards are easily snapped out and snapped back in.

If you're looking to upgrade the speed on your 200LX, the crystal you need to remove and replace is the one next to the Hornet CPU. Just desolder it and replace it with a 32Mhz crystal, or a 36MHz crystal if you're brave. I highly recommend the TechSpeed kit from Times2Tech. It comes with instructions, a specialized replacement crystal, and a very good driver. If you use a different crystal, you'll need a different driver, or your screen will be shifted, alarms will play too fast, and programs designed to run on a slower 200LX may run too fast. There are several drivers available for the 32Mhz crystal. If you don't have one, try this one. The documentation is in Japanese, but I tried it with mine and you just have to put CLKUP32.SYS it in as a device driver in CONFIG.SYS. It probably doesn't have the same features as the driver from Times2Tech, such as the ability to shift between high and low speed with a key combination, but it might work for your purposes. CLKUP31.SYS is also included, and it seems to work the same... For the 36MHz crystal, I'm not sure. It's not that BIG a difference, but you never know...

Anyway, that's about all of interest on the motherboard. Except for the PCMCIA connector, but there's not much you can do with that, so we'll move on to bigger and better things. Such as the screen.

Screen Disassembly

Take off the two caps from the hinges that hook the screen to the main unit. This is easy. Just insert your fingernail in the gap and wiggle it until the caps pop off. Then, gently remove the plastic border from around your 200LX's screen. This is the plastic border with the gold lettering and Quicken and 123 icons on it. Just insert a thin screwdriver into the gap between the border and the case and pry it up a little, then peel it off with your fingers. It's easy to get off and back on, since it's just held on by some sticky stuff. Don't get it dirty! Keep it in a safe, dry place.

Under this are four more hex head screws. Same size as the screws on the bottom. Use either a small regular screwdriver or a .05" hex key to get them out. Once they're out, the front and back halves of the display will come apart a little bit.

To take the screen completely off, let's first assume you have your motherboard out. That's good. Now, looking at the inside of the upper half of your 200LX, you should see the place where the batteries used to go. (There are little battery pictures there.) You should be able to see the little clips holding the round plastic piece that sits as a sort of "hinge" between the screen and the keyboard. Pop these out with your fingernail, or a screwdriver. (Do the ones on the end closest to the PCMCIA socket first. Be careful, especially if you use a screwdriver, that you don't break out the back plastic of the case when prying these out. I recommend using your fingernail.) Once the first few are out, the rest of the clips should pop out with ease. Then you'll have a very long U shaped piece of plastic. Under it you can see the video ribbon cable, which runs all the way across and up into the screen. You can also see a braided metal cable running from a connector in the battery compartment to the screen. These are vulnerable--especially the ribbon cable--so be careful.

To pop the screen open, insert your fingernail into the slot between the front of the screen and the back and run it all the way around. These two halves are also held together by plastic pegs. I broke off two along the bottom on my case, but it doesn't really matter; it still holds together. Still, try to avoid pulling at an angle. The hardest pegs to get out are the ones just under the latch. The latch doesn't have any springs or anything, so don't worry about that. I just very carefully reached under it with a screwdriver and pried until the peg on the left came out a little bit, and then I repeated with the peg on the right. After they were out a little bit it was easy enough to separate the halves with my fingernail. The latch may fall out, since it's not secured in there and just slips in and out of it's slot. A word of warning: remember, if the latch comes out, put it back in before you reassemble the 200LX! :) Not that I have EVER done something like that, of COURSE.

The only part of the 200LX I absolutely DO NOT recommend disassembling is the right hinge. The 200LX's screen is held up (that is, it doesn't flop around) by a "friction clasp" in the right hinge. The hinge itself is held to the case by a metal piece. It's shaped like a rotated L. One peg goes into a hold in the case, and the other (much thicker) peg forms the center of the hinge. The whole hinge has a metal cap on it that holds it together. Inside is a white plastic piece that circles the metal rod. Then there's a spring, and finally a black plastic piece that keeps everything from coming out of the right side of the hinge. If you pull off the metal cap (a very difficult task in itself), the spring will come out, and it is VERY DIFFICULT to reassemble it properly. I had to resort to substituting other materials in there, and it wasn't pretty.

It doesn't matter anyway, because you can completely remove the LCD from the case without opening up the right hinge anyway. And, if necessary, you can pry the screen off of the main case because the smaller metal peg is only held in a plastic hold. It's easy to pry out and push back in.

To remove the LCD, just open the screen's case up from the left, reach in, and wiggle it out. The circuit board behind the LCD is attached to it, so don't try to separate them. Also, the circuit board circles around the hex screw holes, so you may have to pull the screen forward a bit to get it out. And make sure the bottom plastic pegs are out before you try to take the screen out, or they'll hinder you.

Once the screen assembly is outside of the case, it remains attached only by the braided metal cable. The ribbon cable attaches to a circuit board to the left of and behind the assembly you just removed, and that's why pushing on the screen sometimes helps when there's a problem. The contacts are over on the left.

You can detach the circuit board from the LCD face, but not completely. (Or, I guess you could detach it completely, but that would destroy it.) The cable on the right of the screen that attaches it to the circuit board must not be injured, or your screen will not be able to display data. Also, don't injure the plastic strips across the top and bottom. These hold conductive contacts that send the signals to each column. However, you may need to get in behind the LCD itself for installing a backlight, or cleaning, or whatever. To do this, just unbend all of the metal hooks that loop around behind the circuit board. Then you can remove the metal frame which holds the LCD to the circuit board. Be careful! One false move and your palmtop will never work again.

That's about as disassembled as you can get. Reassembly is usually pretty simple; just go in reverse. If I have time I'll post better instructions.

One of my high-priority projects at this time, and one thing many people have shown an interest in, is a backlight for the 200LX. Indeed, it would certainly be nifty to be able to use your HP in the dark, or in sub-optimal lighting conditions. Many's the time I'm trying to type during the previews at the movie theater, and what do I get for my efforts? Nothing but a headache. Currently, I'm using the Flexible Pocket Light from The Palmtop Network. However, this is still bulky and inconvenient, and it doesn't evenly light the screen, and I almost never have the light with me when I need it. Therefore, it seems that a backlight is a really good idea.

Now that that's settled, what sort of backlight is available? You can't just plunk a light bulb behind the screen--that would take up too much power, and there's not room anyway. So what can be done?

At the time this was written, mid-1997, I wrote the following.  Since then, I have been working on a backlighting
upgrade for the 200LX, and am nearly ready to offer it as a commercial product.  These older speculations are left
up here for reference.  Hopefully they'll spark some ideas.

The way I see it, there are several options:

1) Install very thin lights around the border.

This method is probably the easiest. There is a little bit of space for that kind of thing, so if you could get a light that was thin enough, you could probably fit it in there. The problem here is that it is very difficult to illuminate much of the screen from the side. Ever see one of those old calculator watches, that actually used a tiny incandescent bulb to light the screen? That was popular for a long time, but you could hardly see anything on the screen! I have tried this method, and found that it would be difficult, if not impossible, to get much illumination from lights around the border of the screen. (At least, without defacing the palmtop. Remember, all this has to be inside the 200LX...) Incandescent bulbs are probably too short-lived and power consuming to be the solution to the backlighting problem. LEDs are probably better.

2) Install very thin lights behind the screen.

This is more reasonable. There is a thin space behind the LCD panel itself and the circuit board behind it. I have seen many very thin LEDs, mounted on circuit boards, that if glued onto the circuit board behind the screen, would illuminate it quite nicely. Unfortunately, LEDs on the order of thinness that we would need here seem to be fairly rare: none of the LEDs I bought in an assorted pack of 20 from Radio Shack would fit, despite some of them being quite tiny. None of the electronics stores in the Las Vegas area carry LEDs thin enough to fit behind the screen. However, there is also another problem: the LCD itself has a large white sticker over the back of it. This is presumably because the LCD panel is clear, and without this white sticker, you'd be able to see right through it and see the green circuit board behind. I'm not sure if this sticker is reflective, but it seems to me that it would have to be for the display to work. And no light will go through the thing! I got a very bright LED and switched it on behind the sticker and...nothing came through. Therefore, this would probably have to be removed before any measure of effective light could come through from behind the screen.  The best idea would be to replace it with a transreflective sticker that would reflect incident light from the front but also let light from behind come through.

3) Install an electroluminescent panel.

This is the same technology used in Timex Indiglo and Casio Illuminator watches. It is the same technology used to backlight most of the new Windows CE palmtops. The problem with this is it requires a high voltage and a high frequency to light. Also, the panels have a limited life span; they last anywhere from 1000-5000 hours, and they get dimmer with use. There are 200LX's in Japan that have done this. We will all just have to be patient. Or hope that Notebook Supply Warehouse figures out a good backlighting method.

News flash: The reason I mentioned Notebook Supply Warehouse in the above paragraph was because I knew they were working on a backlighting method for the 200LX. They have obtained the Japanese electroluminescent panels and are working on a decent installation technique. However, Times2Tech is also working on a backlighting technique, one which I feel would be much better! The problem with their method is that the cost would largely be determined by the volume of people wanting a backlight.  So let's all write to mack@times2tech.com if we're interested.


A WORD OF WARNING: certain keys on the 200LX are susceptible to breakage.  The space bar and the Enter
key are only held on by thin plastic tabs on the left and right corners of the bottom, which you can see fairly well
just by looking down on them.  If these tabs break, the key will fall out, and even if only one side breaks, your key
will still not be easy to use.  PLEASE make an effort to press in the center of these keys and not to the left or right,
as pressing to one side or the other tends to break the tab on that side.

The 200LX keyboard is completely modular.  If you spill something on it, it can easily be cleaned; if a key won't
press any more, it is fixable.  Even keys which have physically broken off from the frame are fixable to a certain
extent, with Superglue.

First, peel off the overlay.  This is the plastic part that has the words such as "ZOOM," "DATE," and "TIME"
along the bottom, along with the names of the blue keys and the shifted characters above the numlock.  A
screwdriver under the left corner will pry it up, and it can then be peeled off.  Be careful not to bend it too much, or
tear it.  You may need to clean the adhesive before putting it back on.

You will now notice that all of the white keys are part of the same plastic frame, and attached by small plastic tabs.
The numeric keypad is on a separate, black frame.  This frame is held into the 200LX case by numerous small pegs
on the bottom.  In order to pop these out, it is best to open up the bottom of the case, remove the motherboard, and
press out the pegs with a small screwdriver or other tool.  (Be careful about putting dents in the plastic too much.
Although you won't need to look at the pegs, the less you press a metal blade into them, the better.)  Once these
pegs have been loosened, you can pry the keyboard assembly up from the top with a screwdriver or other tool and
pop the whole thing out.

Under this you will find a plastic layer, with small bubbles in it.  These are the actual contacts for the keys; it is
these "bubbles" which produce the characteristic clicking feel and feedback of the 200LX keyboard.  This layer
can be easily removed once the hard plastic key assembly is out.  Under that is another plastic layer, with the
bubble contacts on it.  Under that is some sort of paper insulating layer.

Putting the keyboard back together is more difficult; not because it's complicated, but just because the pegs are
trouble to push back in.  Just take it slow and make sure each peg goes all the way back into the hole.  If you miss
a few, your keyboard will still work, but the keys will look pretty weird, as though they were set at an angle.  Try
not to do that, as it could increase stress on the keys and cause breakage.


This is a disassembled palmtop.  The screen has been removed
from the backing as well.

This picture shows the palmtop with the cylindrical hinge component
removed.  Notice the screen cable which runs through it.

This shows the backing of the screen.  You can see how the cable runs
across the length of the palmtop.  The contacts at the left are where the
LCD connects.

This diagram shows various components of the palmtop.  They are oriented
in the same direction as they would normally be.  (Some of the numbers are
kind of fuzzy.  Stupid JPG format.)
1. This is the speaker.
2. This is the Hornet chip.
3. This is the AC adapter jack.
4. This is the pad where the keyboard connects to the motherboard.
5. This is where the batteries go.
6. This is the LCD component.
7. The keyboard unit.
8. This is where the LCD component presses on and connects to the ribbon cable.
9. These are the components that come out of the right hinge.  The fact that they're not still IN the right hinge is very bad.
10. The screen ribbon cable.  The right end connects to a slot on the motherboard.
11. This is the thin plastic piece that clips around the screen to hold it in.

These are the parts that come out of the right hinge.  The metal post is the main support.  The small part fits into a hole in the palmtop's case.  The spring fits over the large part, and the little black piece goes on the end.  Then the white plastic piece inside the metal ring fits on the end.  If you're interested in this, though, you're probably in a lot of trouble.

A closeup of the bottom of the motherboard.
1. This is the slot for the backup battery.
2. Just to the left of this number is the crystal you'll need to replace if you're upgrading your speed.
3. This is the Hornet chip.
4. This is the screen ribbon cable, which clips into the white slot on the motherboard below it.

The top view of the motherboard, and a bottom view of the keyboard.
The white cable at the top with the black stripes is where the keyboard connects to the motherboard on the white strip down below.
The large circled green thing is the Times2Tech RAM upgrade.  It plugs into a connector on the motherboard on the right side.

The view behind the screen.
The red circled parts are clips you'll have to bend up to remove the circuit board from the LCD panel.  On the left side, though, the LCD panel is connected with a delicate ribbon cable along the whole length of the screen.
Also note that there are more clips than the ones I circled, both to the right and along the bottom.  You'll just have to extrapolate that out once you open the screen yourself.  I'm sure it won't be too hard.  :)

Another view of the screen.  There is a metal cable soldered onto the upper
left corner which must be desoldered to fully disconnect the screen unit
from the keyboard unit.  (The other end is attached to the battery clip.)
In this picture the clips are a little more visible.  They run along the top and bottom.

Copyright 1999, David Sargeant.
Last Updated 1-2-1999

Return to main page Product Reviews Editorials Downloads Contests FAQs Hardware Hacking HPLX.NET Affiliates Home