Hi Daniel,

I´m going to try to describe in my poor english exactly what i did. Unfortunately I don't have pictures for the whole process. What it happened was that I previously (I did not know how to do it) use cyanoacrylate super glues to stick on graphite in powder in every bubble of the keyboard, where I saw it was an erosion marks. Well, that was a big mistake because the blend (which got hard after drying) was to thick and irregular, and when the keyboard was assembled some of the keys did not move at all, and others did not make contact. When I tried to clean it up with isopropyl alcohol, it didn't work. Then I thought that the keyboard was destroyed because that glue agent is extraordinarily strong and every spot was hard.

Next day, I decided to use a mini drill with a spherical stone. I used it very gently in every spot (concave parat of bubble) and when I finished the whole part was completely transparent. Then I bought Graphite paint for re-paint remote controls contacts and with a cotton swab (for inner ear) I stamped (painted) the graphite pain spots, I painted three coats in every bubble (you have to wait half an hour between coats), and the result was perfect.

To repair two keys (the top part with the keys you press to type) they have one of the two supports to the frame that has every key were broken, and I used the same cyanoacrylate super glues to glue them to the frame.

(EMI = Electromagnetic Interference: Communication problems when the HP Palmtop cannot communicate via InfraRed anymore when a mobile phone is near, e.g. in setups where the Palmtop should use a mobile phone via IrDA for Internet access.
Contents of this page:

• Introduction
• Diagrams (schematic and board layout)
• My Measurements

NEWS:

I have bought a used 700LX to study how HP solved the EMI problem there (since the 700LX is designed to work with a GSM phone on top, it must be somehow shielded against the EMI, and tests with ring.com and a seperate GSM phone so the dehaviour of the 200LX and 700LX regarding EMI coulr directly be compared, showed that indeed the 700LX is only disturbed marginally by a mobile phone). The results can be viewed on the separate 700LX page: Click here!

Introduction:

The problem appeared, when the first people wanted to use their HP 100/200 LX to connect to the Internet using the IrDA interface of a mobile phone in the summer of 1999. It is nice to have the ability to simply put the palmtop upon a table, put the cellular phone besides it, and surf the web, download email etc.
Actually it should be possible without problems, because the palmtop has got an IR port, and more and more cellular phones also have an IrDA port which looks to a PC just as a standard modem. The ´internet suite´ WWW/LX by D&A Software is the only software which is able to speak the IrDA protocol over the palmtop´s IR port. Actually the IR port of the palmtop speaks the "HPSIR" protocol which cannot be handled by modern mobile phones. So you have to use WWW/LX if you want to go online via IR.
But you will run into the following problem: The connection is either terribly slow, or it isn´t possible at all to get a working connection.

The people who ran into that problem first were Andreas Garzotto (programmer of WWW/LX), Stefan Peichl and I, Daniel Hertrich. Later Mark Willis, Joeseph Buford and Jerome V. Healy joined us to help. With time I got many requests for help regarding that subject, but a real solution isn´t found yet!

The problem is caused by the following:

Everytime we want to establish a connection to the internet with the mobile phone via infra red (IrDA-protocol by WWW/LX), the palmtop receives strange disturbance signals. These signals are caused by voltages induced by the electromagnetic field surrounding the antenna of the mobile phone.

Actually these signals must have a frequency of 900MHz, 1800MHz or 1900MHz (GSM, PCS), depending on the frequency of the cellular network. But these modulation frequencies are pulsed with a frequency of about 1,6 kHz (maybe that´s only true in my case - I don´t know if the pulsing frequency differs between cellular networks!).
And these pulsing is probably the frequency which causes the problems.
I don´t think that the very high frequency of 1-2GHz causes problems. because this frequency is so high that it cannot be decoded by the decoder hardware of the palmtop (and even is not shown by a normal oscilloscope) - see the pictures below!
But the 1,6 kHz signal is shown and decoded! And it is decoded into many, many characters that prevent the IrDA protocol from working properly.
The signal that actually comes through the photo diode has a pulse frequency of around 10 kHz (depending on the character that was sent by the sending device).

If you would like to test these interference by yourself, you can use Stefan´s software ´RING.COM´. It displays every character received by the IR receiver circuit (also the induced signals) and every character causes a click in the speaker. And the average of ingoing characters per second is measured. So you can see how bad these interferences are in your case. Maybe send as a reference a vcard over IR from your telephone. That will not disturb the IR port, but only the actual IrDA data will be arrive in RING.COM (because the antenna pf the phone doesn´t send anything). Then establish some kind of radio connection (i.e. do a call) and place the phone near the palmtop. You´ll see and hear the disturbances arriving in RING.COM!
You can download RING.COM with documentation  here.

Another experience is that with Siemens phones (S25, S35i), the disturbances are so bad, that most of the times a connection isn´t even possible, but with Nokia phones (8810, 7110, 6210...) you get a connection in most cases. You have to find the ideal distance between palmtop and phone in order to suppress most of the disturbances but keep the IR link working. For Siemens phones, this distance is about 15-20cm, for Nokia phones you can place the phone with a much bigger distance from the palmtop. About 50cm should still be possible. Several people worked out little tricks: For example with the Siemens phones (probably also with others) it helps if you take the phone in your right hand during the internet connection: touch the display with your palm, lay your fingers arund the upper edge of the phone and touch the cak of the phone (where the antenna connection is) with your third and fourth finger. That seems to bundle the emitted electromagnetic disturbances in a way that it doesn´t reach the palmtop anymore.

But of course we want to find a durable working solution!
First I thought, the right solution would be to build a high pass filter into the circuit of the IR Receiver to filter out all high GSM frequencies.

I thought we should replace the component no 7 (see picture below) by a properly dimensioned high pass filter. I tried this. But without any luck! :-(
I tried to replace component no 7 with different capacitors of values 150 pF up to 330 pF (My calculations showed that  220pF  is the right value to drop 1,6kHz signals by approximately 15dB and leave the 10kHz sinals untouched. With a filter of 1st grade, a higher attenuation of the 1,6 kHz signal is not possible -- the filter of 1st grade is built by the inserted capacitor and the resistor to ground (no 12 and 13) with a value of 100kOhm + 6.81kOhm = 106,81 kOhm).

Before I did these tests I thought that the GHz-frequencies directly caused the problems and inserted several low pass filters into the receiver circuit. None of them worked)

One solution that already works in some palmtops is to connect pin 2 of the photo diode (the right one, if you watch the diagram below) to ground. It´s not such an elegant solution, because it drains extremely much power and we don´t know if it can hurt the circuit. And it doesn´t work in every machine. About every third machine we tested that ´low cost solution´ in wasn´t affected by the EMI anymore. The other machines couldn´t at all use the IR port anymore. We don´t know why. But Stefan used this solution for about half a year successfully and his palmtop survived it.

Drawings (schematics and board layout)

The circuit board layout with component numbers (description of the components below):

The components of the IR receiver circuit:

PD: the photo diode
1:    R = 21,5 k
2:    R = 21,5 k
3:    Transistor KST 5179 or 2N 5179 by Samsung (pins see below) (Data sheet (PDF, 50kB) downloadable here!)
4:    Transistor KST 5179 or 2N 5179 by Samsung (pins see below) (Data sheet downloadable above (=part #3)!)
5:    C = xx xF (value unknown)
6:    R = 215 R
7:    C = 0,01uF (marking "KA4")
8:    C = ´685´
9:    C = ´105´
10:  R = 10 k
11:  R = 21,5 k
12:  R = 6,81 k
13:  R = 100 k
14:  IC ´TLC372C´ by TI  description here (HTML with llink to PDF data sheet)

The pins B,C and E of the Transistors 3 and 4 are placed this way:

  ------
B O    |
  |    |
  |    O C
  |    |
E O    |
  ------
 

The circuit diagram of the IR receiver (self-explored by Joeseph Buford and me):

My measurements

I made the measurements under the following conditions: An opened 100LX lying on the table, the Siemens S25´s IR port and the 100LX´s IR port are facing each other with a distance of about 3 cm.

You can see the arrangement here (on this picture the S25 is a little bit more away from the 100LX than 3 cm):

The following picture shows my measurements of the signal voltage of an IR-received character (measured at pin 3 of the 372 chip no. 14) without any interference.

Horizontally, one division is 0.2ms, so the frequency of the pulses is approx. 10 kHz
Vertically, one division is 2 V, so the peaks are approx. +/- 1V
 

The following picture shows my measurements of the voltage induced by the S25´s electromagnetic field:

with the same scalings of both axes as the picture above.
The signal has got a frequency of about 1.6 kHz (period cycle is abt. 0.6 ms).

If you would like and/or feel able to help, ideas are greatly appreciated by: Andreas Garzotto, Stefan Peichl, Mark Willis, Joseph Buford, Jerome V. Healy, me and many, many other users of the HP 200LX!
Please email me! I´ll forward your idea to the others.
Thanks to all who help(ed) us and to all who will help!

Contents of this page:

• Introduction / where to let the palmtop repair
• Broken latch
• The hinge crack
• The hinge is too tight or too loose
• The screen: Missing pixels and other problems
• Some or all keys of the keyboard don´t react anymore
• Other case cracks

Here is the page that many hardware hackers will like: The process of dismantling the palmtop

Introduction / where to let the palmtop repair:

This page is intended to give you advice if your HP Palmtop is broken.

If you want to let your palmtop repair professionally, you have two options: 

• Thaddeus computing in USA repairs palmtops for a flat rate, regardless of the defect. They have excellent service and turnaround time, you even get warranty on the repaired device. They also buy used units.
  
  
• Another option for you is to use my repair service. Please contact me to get an individual offer. It helps, if you describe the defect as detailed as possibile in your first email, ideally providing photos or a video showing the symptoms of the defect

In case you decide it is not worth to repair the palmtop anymore, please do not throw it away. It certainly contains valuable spare parts. In that case, please submit an offer for me to buy this machine.

If you need advice how to repair a palmtop yourself, read on:

Of course I cannot cover every imaginable defect, so I´ll describe the most common problems and the problems I´ve had myself. Since HP discontinued the 200LX palmtop, it becomes more and more important to repair broken units, because it will be difficult to find used units in good shape. 

For some of the repairs, you should be familiar with opening the palmtop´s case and taking it apart. For some repairs you even have to take the screen out of its shell. So if you have doubts, rather ask a friend who is able to do this quite complicated job for you.
Warning: You can take almost the entire palmtop apart, you´ll get it back together if you know how you took it apart. But there are a two exceptions:

The right hinge and the screen:
1. The right hinge: Don´t ever take the right hinge apart! Don´t remove the metal ring that holds the hinge together! You probably won´t be able to reassemble it, and that would result in a nearly unusable palmtop! If you want to remove the screen, you can do it leaving the hinge intact. Remove the four Torx-6 screws and carefully bend the screen part of the case apart and take the screen out of it. The screen is only lying in there, no additoinal screws, and the electric contacts are only pressed onto the screen by the two case screws on the left side which you have already removed.

2. the screen itself: If you have taken the screen out of the case, the only thing you can do is to separate the electronics board from the LCD by bending the little metal latches away from the circuit board. But don't ever remove the flat cable that goes from the electronics board of the screen to the LCD glass! That would let the screen die forever! Additionally, it is very difficult to get both screen halves back together; it is a matter of 1/10th mm! SO rather avoid that.

What you will need when doing your first repair job, is advice about opening the palmtop. I have written an article about the process of dismantling the palmtop. There is another source for advice for this:
David Sargeant wrote a page with instructions guiding you through the process of opening the palmtop and even doing hardware upgrades. Click here to read these instructions.

Let's now talk about the actual repairs:

Broken latch:

The latch which holds the case closed if you put down the screen lid gets easily broken. What breaks is not the latch itself, but very thin plastic springs that are responsible for the latch to flip into its original position after you pressed it to open the lid.

It is nearly hopeless to try to glue the spring back to the latch. It will break again sooner or later.
But there are some ways which enable the latch to work again.

1. Use a piece of a rubber band and sqeeze it into the gap under the latch. Maybe cut ittle triangles out of the rubber band, so that it is not so strong.

2. The solution I chose: A drop of silicone, which is actually used to make tight the gap between your bathtub and the wall, will do the job very nicely. You can use a screw driver to work the silicone into the gap under the latch, Just be sure to wipe away any silicone that remained outside. Let it become hard 12 hours with the latch fixed with adhesive tape or something like that, and voila: You have a working latch again.

3. Also a small piece of foam rubber (abt. 13mm * 8mm and abt. 1-2mm thick) can do the job very effectively. I have one palmtop repaired this way, too. Looks not as ugly as the above solutions and works very well.

The hinge crack:

Sometimes the case right above the right hinge of the palmtop breaks due to the strain if you open and close the palmtop frequently. This type of defect is typical for the HP 200LX and appears quite often. It is usually called the "hinge crack". The hinge crack is forced by a hinge that's too tight (See next item!)

Some people simply wait until the crack is wide enough and then put a little(!) drop of superglue or epoxy glue into the crack. That seems to work if you use very good glue.
However, the chance that this fix breakes again is big. There are other approaches, Alan Striegel used a small metal plate to reinforce the hinge, his results are shown on his home page. I have also tried this approach and so far I can tell it seems to be very reliable:

A nice 100LX user, Thomas Mahoney Jr., provided the method he used to successfully repair his hinge crack:

After using 2-part epoxy to reglue my broken hinge halves, I test fit the spring to make sure it was going to fit. Use an X-acto knife to smooth out the epoxy that may have entered the inner hinge area. CUT the hinge spring to about 75% of its usual length with a pair of diagonal cutters, so that you do not need a lot of force to compress the black ring onto the plastic hinge halves. Once all of the hinge pieces are in the correct order and in the hole, I used 2-part epoxy to glue the black ring onto the repaired hinge. The epoxy also acted as a "rubbing" dampener, that is, it makes it harder for the display to flop/fall down since the friction of the epoxy in the area of the right hinge against the hinge tube. The epoxy on the outer hinge also makes it harder for the hinge cap to come off and tightly grips the hinge assembly. Once the epoxy is dried, you may have to use an X-acto knife to cut away undesired epoxy that may be blocking the hinge tube from going back into position and/or cut epoxy away from the outer hinge so the hinge cap can slide on. I had to cut the hinge cap open slightly in order to make it slide onto the hinge. The hinge works good. I actually needed a drop of lubricant to loosen it up slightly after this repair.
Thanks for the dismantling guide. It's great!
Have a great day,

Tom

The hinge is too tight or too loose

If either the hinge is too tight (danger of hinge crack) or too loose (screen falls slowly back while you are working), you may be able to fix that (it does not always work!):
Remove the cap from the right hinge (only the right hinge contains the mechanics). You can do that by carefully prying it off with the nails of your two thumbs while the screen lid is opened with an angle of 90 degrees to the keyboard.

What you see then is a metal shaft in the center and plastic parts around it. The hinge consists of a spring which presses a little plastic cone onto a metal ring (which is on the side you cannot see because it's in the tube). The black plastic you can see directly around the metal pin is the back side of the spring with its plastic anchor. Now you have to adjust the friction of the cone to loose / tighten the hinge. You can do that by using very little amounts of either a lubricant (to loose) or Isopropanol alcohol (to tighten the hinge). Use only a very little drop of the lubricant and work the hinge a few times by opening and closing the lid. Of Isopropyl Alcohol you can use larger volumes. I suggest to use a syringe to apply the lubricant or alcohol.

Caution: Some people reported problems with some lubricants which seem to attack the plastic material! WD-40, for example, must never been used! And remember: Don't ever take apart the right hinge, except you know exactly what you're doing!

The screen: Missing pixels and other problems (and: Doublespeed upgrade!)

If you don´t see anything on the screen, as if the batteries were dead, but you know they aren´t, it is most probably not a screen problem. It may be a software problem. Take out all batteries, press the On key for a few seconds, then let the palmtop alone for 24 hours (so all electricity can vanish). Then put the batteries into the palmtop again and see if it works now. If now, it may be an electrical problem.

If the screen shows weird characters on boot-up or if the screen contents are shifted by about two columns to the right and the two left columns show flickering nonsense, the screen is not defective, but your palmtop is double-speed upgraded! To make things look well again you need a driver. If the double-speed upgrade has been installed by Times2Tech, use the driver by Mack Baggette. The following picture shows a typical double-speed-without-driver screen:

It can sometimes be much worse, so that even the characters are not readable anymore.

To be sure you have a double-speed upgraded palmtop, you can also enter the self-test mode of the palmtop (only if the screen is readable, otherwise you cannot read the self-test output!) using Esc-On to switch it on instead of just On. Then do the "Timers" test. If the test is not successful, the palmtop is upgraded. (Warning: Never do the RAM-Card test if a flash card is in the slot, this test is only for SRAM cards and can destroy other cards!)

If you look through the backup battery tray, you may see if a double-speed crystal is installed. If on the silver cylindrical component behind the tray is written 158 CP52, it is an original single speed palmtop, if you see F31.673, the palmtop has been double-speed upgraded:

If you see nothing written on the crystal, you either have to open the palmtop to read the crystal model number, or run the built-in timer self-test: Press Esc-On to switch the palmtop on, and if you can read the screen well, go to Timers test and press enter to execute it. If it fails (output: time bad), probably a double-speed upgrade is installed. If you cannot read the screen at all due to strange characters, you can be quite sure that a double-speed crystal is installed. Load the above mentioned driver and the screen will be readable again.

If lines or blocks of the screen are missing, flickering or black, or if the whole screen is black or white, there may be a defect.

There are various typical scenarios which I try to describe here. It heavily depends on the symptoms where you will most probably find the problem: 

If the whole screen turns black or white, flickers wholly or block-wise, or something like that:

Maybe only the contacts between the screen cable and the screen itself are loose: Switch the palmtop on so that you see a picture which lets you see problem and press on the area marked in the picture below.

Does that fix the problem temporarily? If yes, you should pry off the screen cover on which is written "200LX" and so on and then fasten the two Torx-6 screws on the left side of the screen. If the screw fastening is not enough, you can probably use a few layers of paper to make the pressure contacts under the screws stronger. If these contacts aren´t the problem, maybe the cable which connects the screen to the motherboard is damaged or not properly attached to the motherboard connector.

If you have missing pixel lines (rows or columns), but if only every second column in a certain area is missing

(e.g. as you can see on the picture below) this is most probably caused by IC contact problems. Since all the mechanical stress when opening and closing the LX is only applied on the right side (because only the right hinge contains the relevant mechanics), mostly contacts on the right side are affected, and these are responsible for the columns of the right part of the screen.

A failure of that kind can look like this (type "On" and the slash "/" to invert the screen, so it becomes obvious which lines are missing):

 I was able to fix such a screen durably by resoldering the pin rows of some of the SMD ICs on the screen´s circuit board which have become loose.

The following pictures show a removed screen module with the ICs on the back. There is no way to tell without tests which of the pin rows may be loose. You have to try that by connecting the screen to a motherboard and pressing gently onto some ICs and their contacts or using a small screw driver to short-circuit the contacts one-by-one carefully while you observe the screen. Please note that you should use real SMD soldering equipment (a soldering iron blowing hot air), otherwise you need an extremely sharp soldering tip and a very calm hand.

 Here you can see the principle how the ICs are wired on the other side of the circuit board (so you can understand which columns depend on which IC contacts):

 However, if you have a screen which looks like this on the back:

You are out of luck, because these kind of screen has the ICs on the other side of the PCB and if that wasn´t bad enough, these ICs are fully covered and don´t have any legs which can be resoldered. But on the other hand, these screens are probably much less prone to this kind of failure. Another problem may be a too loose pressure of the screen glass to the conductive rubber band which connects the circuit board contacts to the contacts between the screen glas layers. But that happens only rarely. This can be fixed, too, but I only recommend that if you have good fine-mechanical skills and if this screen is not your only one - you could damage it forever with the following procedure:

There are metal latches which press both screen parts together. A pair of such latches is marked on the following picture: 

You can first try to fasten these latches in the area where pixel columns are missing. If that doesn´t help, you have to separate the two parts of the screen and clean the contacts of circuit board, rubber band and the glass contacts carefully with alcohol and then reassemble it. The reassembling is tricky, because you have to place the both parts horizontally exactly as they were before you separated them, otherwise the contacts of circuit board and screen do not fit. Although the metal frame helps with that, you cannot rely entirely on that frame.

First, bend the metal latches straight so that they don´t press the parts together anymore. Take care the you do not break one of the latches. 

Now you can remove the entire metal frame in which the two parts are embedded and pressed together.

Don´t separate the LCD from the circuit board yet, but apply some markings on the rubber bands and on the side of the circuit board, so you can later adjust them horizontally 100% precisely again.

Then carefully seperate the two parts, but note that they are still connected by a conducting adhesive tape on one side, this is for the horizontal lines and cannot be removed, otherwise you damage the screen permanently and make it totally unusable! Also make sure the white rubber bands remain on the LCD glass. This makes it way easier to reassemble the screen later. The following pictures show an opened screen:

Screen with metal frame still mounted:

 Screen with removed metal frame: You see the white conducting rubber bands on the long sides and the yellow conducting adhesive tape on the short side.

 Seperated screen parts: Do never remove the yellow conducting adhesive tape (actually a ribbon) on the short side and be very careful with it! Do not apply any force to it! 

Now you can carefully clean the thousands of contacts on the circuit board and on the rubber band. Lift the rubber band only in these areas from the screen glas, where columns are missing, and clean the contacts there, too. Then reattach the rubber band to the glass and reassemble the whole screen. Take care you adjust the two parts horizontally exactly the same way they were adjusted to each other before, otherwise you will not get a valid picture, if you will get one at all! Many missing columns in a pattern which looks like an interference pattern can be the result.

Be sure to bend the metal latches again so that the two parts are pressed together with appropriate force.

If a block of consecutive rows or a single row is missing:

This can be caused either by bad IC soldering contacts, or (which is the worse case) by a defective ribbon cable - the yellow one on the right short side, which connects the LCD glass body to the circuit board of the screen module.

First try to find loose IC contacts, as described above. If that is not successful, take the screen module apart as described above, prepare a flat iron (highest heat level), put a bunch of paper strips under the contact row of the LCD on the right, where the yellow ribbon cable connects, to support the LCD glass mechanically, then press the flat iron gently onto the ribbon cable, moving it slightly, to melt the plastic and glue a little. After a few seconds, remove the flat iron and let the screen get cold again. I was able to fix some screens using this method. But it is risky, if you apply too much heat to the ribbon cable, it may be damaged permamently. In case this didn´t fix the problem, try the same on the contacts on the other side of the ribbon cable (on the circuit board).

Some or all keys of the keyboard don´t react anymore

Most likely the pressure contacts which connect the keyboard to the motherboard are not pressed strongly enough against the motherboard. These contacts are placed in the area under the menu key, the right shift key, the zero key and the dot key. Try to press the two parts of the palmtop´s shell together in that area and see if that fixes the problem.
If it only fixes it temporarily, you should try to fasten the screw under the plus key (from the bottom of the palmtop).

If that also doesn´t help, it may be necessary to clean the keyboard contacts to reduce resistance between the two contact counterparts. For that, you´ll have to open the palmtop. Click here to read how to do that. Be very careful when cleaning the keyboard foil contacts with alcohol or any other solvent. The contacts are build by a thin graphite layer, which is easily rubbed off using solvents. Clean them only once, and with only slight pressure with a soft tissue and some alcohol. Don´t worry about the black stuff rubbed of the contacts: It´s probably no dirt, but the graphite itself. So do not rub until no black stuff is rubbed off anymore!

The contacts on the motherboard can be cleaned as usual, using isopropyl alcohol and a tissue. These contacts are made of copper, so they cannot be rubbed off using a tissue.

Other case cracks

The hinge crack is by far the most common crack which appears on the case of the LX. However, there are a few more positions which the case breaks easily at. For example the little plastic "bridge" on the back between the battery cover and the keyboard part of the lower case shell:

I have no idea how this can be fixed the best way. I would try to take the shell apart, put epoxy glue into this crack, wrap it with adhesive tape until the glue is hard, remove the adhesive tape and then reassemble the palmtop.

Interesting links:

• Looking for a successor for the HP Palmtop? Have a look at the OpenPandora and Pyra Linux Palmtops!
  
  
• If you need repairs, upgrades and spare parts: Please contact Michel Bel (Netherlands, Europe) or Thaddeus Computing (USA).
  
  
• Join the community: There is still (or again, after a pause) the HPLX mailing list, where still a lot of helpful people are around. Me included (as of 2019/2020)
  
  
• If you need software for your Palmtop, browse the S.U.P.E.R. palmtop software archive. In case the main link does not work, try this mirror: http://mizj.com/

My service:

hermocom was one of the last few supporters worldwide for the MS-DOS-based Palmtop PCs made in the 1990s by Hewlett Packard.

These are the HP Palmtop PC models 95LX, 100LX, 200LX, 1000CX and the OmniGo 700LX.
I can mainly help with the 100LX, 200LX and 1000CX models. The other ones you can ask me about, too, but I am not too experienced with them. 

• Although "hermocom" does not exist anymore, I am still here, if you have a question.
  
  
• Have a look into my HP Palmtop knowledge base, a collection of articles about various topics, which may answer some of your questions already, or give you new ideas in order to find solutions.
• Software packages and drivers in the HP Palmtop Software download area.
  
  
• Please contact Michel Bel (Netherlands, Europe) or Thaddeus Computing (USA) for repairs, upgrades and spare parts.

   

Until 2014 I also offered:

• Repair service (worldwide) 
• RAM upgrades 
• Speed upgrades 
• Backlight upgrade kit
• Spare parts, accessories and special offers

 Since my interests have moved on to new topics (e.g. photography), I don't have the time anymore to care much about he HP Palmtops. But I still appreciate them as probably the best ultramobile computers, that have been available by now. :)

1. Make sure the Palmtop is switched off and has good batteries
   
   
2. Make sure there is no FLASH-based memory card inserted (this is for safety: Attention: NEVER EVER use the "Plug-in RAM card test", while a Flash (ATA flash, Compact Flash) card is inserted. This test is only meant for SRAM cards and it will destroy flash-based cards (or at least their contents).
   
   
3. Hold the ESC key pressed and shortly press the "ON" key. The Palmtop will switch on and directly boot into the self-test menu.

Note for Doublespeed-upgraded Palmtops: If you have the doublespeed upgrade installed, the menu might be unreadable due to distorted font, because the doublespeed driver is not loaded at that stage. Connecting the Palmtop to an AC adapter might help in this case to make the menu readable. If that doesn't help, you would need to use the test "blindly", as far as this works. E.g. the keyboard test can be used blindly, if you know how it works.

If the menu is readable, but you need to check wether you have a doublespeed-upgraded Palmtop or not, use the "Timers" test:

• If the results are in the 10.000 range, 10.700 to 10,913, it is single speed
• If around the 21400, it is a times2tech exact double speed.
• If around 21840, it is a 32.000 Mhz double speed version.

Note: The keyboard test may need a little explanation: During the test there are numbers displayed that denote the key you need to press in order to test it. The numbers mean: 

First place: key row
Second and third place: key column.
E.g.: 104 means "1st row, 4th column", i.e. "Now press the F2 key".

You are asked to press all keys consecutively, left to right and top to bottom. A high beep means "key OK". A low beep means "You pressed the wrong key" and no beep obviously means "key not pressed". If you pressed the key but don't get a beep, it  thus means "key is bad". ;-)

If you see this "RAM4 bad" message or something similar, you may just have destroyed your flash card with the RAM card test:

Another HP200LX Broken Latch Fix

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.

INTRODUCTION

I have never met or heard of an owner of a HP200LX who does not have a broken latch problem. I have only seen an original working latch once and it was in a practically unused HP200LX.

The 'latch problem' seems to be, along with the omnipresent and hideous hinge crack and broken battery covers, the most common problem encountered (sooner or later) by all HPLXers. I am, of course, no exception to these (only the last two, fortunately) problems which I personally find difficult to forgive HP's engineers for. Much more so if we take into account the amount of money one of these little marvels went for when they first came into the handheld computer market.

There are a quite a few fixes and/or solutions to the broken latch problem out there and this is just one more of them, just another idea. It takes a bit more time, requires some knowledge/experience in taking apart the HP200LX, manual dexterity and a certain knack for fixing things in general. It involves more risks but, in my opinion, the end result justifies all the trouble.

REQUIRED DISCLAIMER

If you are reading this, chances are that you have already read the previous page. If not, then please do read it, particularly this same section.

I won't go into the details of how to dismantle a HP200LX to fix the latch as it has been thoroughly documented by two very experienced LXers: Daniel Hertrich has done it here and David Sargeant has done it here.

Please do take the time to read what they have to say about taking apart, hacking and repairing a HP200LX, generously sharing their experience with the rest of us.

WHERE I GOT THE IDEA FROM

When I got my HP200LX, one of the the first things I did (I'm a 'it's not yours until you take it apart person') was take it apart and this put me in contact (among other interesting things) with the latch problem. At first I did not see it as a big issue, but in time and with everyday use I eventually came to the conclusion that it was not a good thing to have the latch in that condition with the screen 'open', so to speak.

Or maybe it was just the itch to do something more with my HP200LX ....

So I started looking for a way to get the latch in working condition again. Unfortunately, none of the solutions I found (silicone blob, rubber band, foam, etc.) did the job very well. The latch never closed properly and thus the screen was not secured in it's closed position.

I really hate to say this, but after taking it apart and seeing how the latch was 'supposed' to work, I concluded that HP's design for this latch is really not a good one, to say the least. Certainly not what one is (was?) used to expect from a company such as HP and in something as expensive as a HP200LX.

THE PROBLEM

The 'spring back' force the latch relies upon to stay closed is actually provided by the same thin plastic rods that form the latch's hinge (a horizontal pivot) through a couple of 90º bends at their ends which are held in place and kept from turning along with the pivot when the latch is pushed on.

So every time you push on the latch to open the HP200LX, the thin plastic rod that serves as a hinge is subjected to torsion (certainly not for this type of material) with the end result being that when the plastic reaches it's fatigue limit and breaks, you not only lose the 'spring back' force needed to keep the latch closed but you also lose the hinge the latch pivots on. If I didn't know better, I'd say that it was designed to break after some use.

Which is exactly what it does. ;-/

The problem is then twofold. In order to get the latch working properly again, two things have to be recovered: the latch's 'spring back' force and the hinge the latch pivots on. I think it is the lack of this hinge that keeps the other solutions available from working properly.

THE SOLUTION

Close inspection of a broken latch and it's lodging will show all that I've described above plus one thing I had not noticed before: a small cone shaped protuberance on the surface of the underside of the latch.

Being most probably the injection point for the mold used to make the latches, it is (by design) right in the centre of the latch and thus in a perfect place to secure a coiled spring in order to give the latch the force needed to remain locked. Curiously enough, when the latch is in place, this little cone shaped protuberance is situated right opposite the centre of a square flat piece of plastic which is part of the upper side of the screen bezel and serves as a perfect point of support for the spring to work against.

Couldn't be better.

Here's a shot showing what it would look like once in place:

How it ends up will obviously depend on the type of spring you use. I used one of the battery connector springs from the mainboard of a dead Palm III and cut it progressively shorter till I found the right combination of force and radius. You need for it to exert just enough pressure but you don't want it to be so large that it shows outside the bezel or keeps the lid from closing.

I'd say that most any old electronic appliance using 1.5v AAA batteries can provide you with an adequate spring that, being properly designed for the job, won't break after just 250 cycles. 8-/

Depending on the spring used, you can glue it on to this small 'cone' or try to have it stay in place by means of it's own pressure. I put a small drop of a cyanoacrylate based adhesive (Super Glue, etc.) to help it stay put, especially while I was assembling the lid.

Now, the spring by itself will not solve the latch problem. The lack of a hinge on the latch's horizontal axis for it to pivot on does not allow the catch to hold in place as the whole latch is pushed upwards and not just the part with the catch.

To fix this (actually the trickiest part of this screed) you have to practise some surgery on the latch itself. It is the trickiest part because it is not possible to use just one single (and very easy to align between just two points) piece of plastic or wire to rebuild the hinge: it just won't fit in place due to the existence of two mounting tubes which are used to fix the screen bezel in place.

All these descriptions I am induging in may seem a bit confusing if you haven't taken apart a HP200LX's lid and screen bezel, but with the parts in front of you it all makes sense right away. A look at David and Daniel's thoroughly documented instructions will quickly dissipate any doubts you may have.

The thing is that you have to manually align two separate pieces of plastic or wire along the same axis and fix them in place by melting the plastic using heat or with resin, epoxy or whatever else you can come up with.

I reconstructed the pivot on the latch using a piece of steel wire I had left over from when I made 'Z' type springs to hold down coolers on top of Pentiums with broken ZIF sockets and a combination of heat and resin to glue them in place.

If you are lucky, the end result will look much better than the frankenhatch I was able to come up with. It's damn ugly, but it goes unnoticed once in place and most important, it works quite well.

This is a close up of one of the ends:

Here's a view of the finished frankenhatch. Notice that the wires are not exactly aligned along the same axis (the ideal situation). In this case, it does not seem to affect the way the latch works, probably because they're off by just a bit. As always, ymmv.

Once in place, this is what the fixed latch looks like from the outside. Notice that it sits flush with the rest of the cover/case whether it is open or closed:


Here you can see the spring once the latch is in place:

That's all ... ;-D

Copyright © 2008-2010 Carlos Izzo Videla. All rights reserved.
Page now hosted by www.hermocom.com

95LX user Robert Rozee from Christchurch, New Zealand, provided info on how to fix the common fault that the 95LX reports "low battery" although the inserted batteries are fresh and full:

Hi,
    I've just spent the evening fixing the 'Low Battery' fault on an
HP-95LX a friend gave me last week. Your website
(www.daniel-hertrich.de/95lx/) provided invaluable information - the
photos showed me the polarity of some components I had removed without
taking note of the polarity  :-) 

I've searched the web a bit about the 'Low Battery' fault that seems to
eventually plague most 95LX's, and the only clue as to a repair I found
was a guy who said his unit came back with a note about replacing a
capacitor. After quite a bit of experimentation - removing and replacing
small tantalum capacitors - I now know which one... I thought you might
like to add the information to your website.

The offending capacitor is a 0.1uF tantalum device located just above
the blue resistor pack that is to the right of the lower RAM chip (and
to the left of the keyboard connector). It is visible in this photo:


The capacitor is the yellow part (I'm not sure how electronically savvy
you are!)

Removing the capacitor, and the 'Low Battery' messages go away and the
'battery meter' in setup shows full. Replace it, and the messages
returns when powering up and the battery meter reads empty. Pretty
conclusive. In my unit I replaced the device with a 0.1uF chip ceramic
capacitor, but I suspect that it could simply be left out without much
problem.


Hopefully this info can help some other old calculator collectors out
there - it's a pity no one found the solution back in the 90's!!

---

Attached are a couple of
photos of my HP95: one before the component was replaced, with an arrow
pointing to it; the other after it was replaced, with a red mark on the
body of the new capacitor.

I just grabbed a ceramic capacitor of the right value out of our parts
store here at work, but a suitable component would be:

Kemet C0805F104K5RAC
http://nz.farnell.com/jsp/search/productdetail.jsp?SKU=1288272
The only important details are 0.1uF and small enough to fit. The old
component is polarized (the end with the bar is POSITIVE), while the
replacement (ceramic) part is not. Note that this is a suitable
replacement ONLY for this one tantalum capacitor - I tried replacing
them all and got into a right pickle! (this is where the photos on your
site saved me)

Before:


After:

How to disassemble the HP 100LX, 200LX and 1000CX Palmtop

Introduction:

This page gives you an idea about the steps necessary to get to certain inner parts of the HP 200LX palmtop. Since the hardware is almost identical, this article also applies to the Palmtop models HP 100LX and HP 1000CX.
The steps have to be executed in the order shown here; you cannot take apart the screen without first having to take apart the whole 200LX body, for example.
Do everything very carefully, and be aware that you risk the life of your palmtop, if you take it apart. I will not be responsible if any of the steps described here will damage something, for me this procedure works, and if it doesn´t for you, it is not my fault! Do not do anything described here if you do not feel comfortable with it! It is tricky, and if something goes wrong, you can easily make the palmtop totally unusable.

All data will be lost after the process! So back up everything before you open the palmtop.

The following picture shows how the HP Palmtops are assembled. The picture actually shows a 95LX, but the other models (except the OmniGos) are very similar.

Main part:

Begin with a clean table surface.

You need the palmtop, a credit card, a Torx-6 screw driver and some small ordinary blade screw drivers (not shown on this picture).

First, remove all removable parts (IR / backup battery cover, backup battery with its holder, then the battery door, the main batteries and of course the PCMCIA card, if there is one in the slot).

Remove the four bubber feet using a small blade screw driver or your finger nails.

Remove the four screws under the rubber feet with the Torx-6 screw driver.

If you later want to remove the screen: Remove the two hinge caps now. Open the palmtop so that screen and keyboard have an angle of 90 degrees, then use your thumb nails to apply force behind the hinge caps. It may be necessary to wiggle them a bit:

Close the palmtop again, now we will open the body. You will need the credit card soon. Make sure it is accessable with your right hand. Begin to pry apart the body carefully in the corner where the PCMCIA eject slider is.

Put the palmtop onto the table so that the backup battery side shows down and the PCMCIA slot shows up.
Now take the credit card, stick it a few millimeters into the gap (only a few millimeters!! Not more than necessary, because you would damage the keyboard cable with the following...!) and slide it slowly down through the gap in the direction of the right palmtop side. Stop when it is in the posistion shown in the picture below and lever the two body halves apart at this point. Here is the position where the two halves are kept together with the strongest force, because here is the screen-mainboard connector, which is a pressure contact.

Now the front side of the palmtop body should be open a few millimeters. That was the most difficult part.
But in the range of the battery compartment the body halves still hold stronly together!

Pry them carefully but also forcefully apart exactly where the plus pole of the batteries show to. But seperate them first only for some millimeters, because...

...it may be that the battery contacts still stick in the motherboard battery connectors. You can see this through the gap. If this is the case, use a small screw driver to flip them out. See the right picture: The right one of the mainboard connectors (left and right side of the big yellow capacitor) still holds a battery contact which has to be removed.

Now you can safely separate the two halves.

If the battery contacts had to be manually removed from the motherboard, they are probably not in their right place in the bottom shell anymore. Press them back into their place: The left image shows that the right battery contact is not in place.

Now we can almost remove the motherboard. Only the screen cable has to be detached from the motherboard first. Use a small screw driver to open the connector (left image shows closed, right one the opened connector). When the connector is open, you can easily remove the screen cable.

Now take the mainboard out of the body. It is only lying there, no further screws.

Still not enough? You want to remove or even take apart the screen? ;-) Okay. Here we go:

First, we must separate the screen case from the body. For that purpose, we first have to take out the white screw-like disks in the battery compartment. "Screw" them out by spinning them with a screw driver, no matter in which direction, by exactly 45 degrees. Then you can remove them.
Note that there are one or two grooves on one of the four sides of each white disk. When you reassemble the palmtop, these grooves should point into the same direction as they did before you removed the disks, i.e. towards each other. This is for the screen cable to have the needed space.

Flap up the screen to 90 degrees, then press the hinge tube (the long black tube between the hinges) gently together and pull it away from the body. Again, only a few millimeters first, otherwise you could damage the screen cables. Begin on one side and proceed in the middle, later pressing and pulling on the other side. On the right side the hinge is mounted on the case body with a meetal pin in a hole of the case. This could need some more force to be pulled out, sometimes it's easy. Don't apply brute force. If necessary, push from the other side of the hole with a small tool.

When the tube is separated from the body, gently slide out the orange screen cable through the hole and even more carefully slide the silver ground contact into a position so that you can stick it through its hole out and remove the screen entirely from the body.

Now remove the screen cover from the screen. Lift in in one corner carefully with a small screw driver and begin to pull it off from that corner. Be careful, since you need a lot of force to pull it off.

You will now see four more Torx-6 screws. Remove them. It´s easy.

To separate the two halves of the screen case you need the credit card again. Begin in the upper left corner, take most care in the range of the latch, since the case plastic is very thin there, then pry the halves apart on the bottom side, but stop before you get to the right hinge! Don´t ever take apart the right hinge and take care you do not break anything in the surrounding of the right hinge!! Also take care with the little latch which holds the palmtop closed when it is not in use. It has extremely thin plastic springs which can easily break (the picture below shows a broken latch)..

Try if you can lift up the screen easily on its left side from the flat cable connector. If not, you have to lift it gently using a screw driver. But take care not to damage anything on the circuit board. Now you can bend the two case halves apart and take out the screen. On the right side you will have to lift the screen up from the right hinge, don´t force it into the left direction, but lift it up!

Now you have removed the screen. Do you really want to do more? Take apart the keyboard?? Well, if you are sure...

The keys are held together by a plastic grid, and this grid is mounted on the LX body by many, many little plasic pins. You see these plastic pins from under the keyboard as little black (number pad) and grey (other keys) dots. You will have to push every single pin with a small centre punch or similar out of the hole. Once you have done this, you can lift up the plastic grid with the keys.
You can remove the keyboard cover (where the additional meanings for the keys are printed onto) only in a convenient way before you pushed out the pins. So do it before or never. As with the screen cover, use a small screw driver and begin in one corner. Then pull it off entirely.

Once you have removed the cover and the key grid you will see the different foils involved into the keybaord functionality. I have also removed the contact foil for you (the white thing), which should not be necessary in general, and the following picture shows all keyboard components in the order of appearence from the top down (on the picture from left to right):
Keyboard cover, key grid, bubble foil, distance keeper foil, contact foil with motherboard connector.

Here are detail pictures of the keyboard components:

And here you see an overview picture of the entire disassembled HP 200LX:

Well, that´s it. Now reassemble everything. You can do it in the exact reverse way you disassembled the LX.
If you are interested in disassembling the screen module for repair or for backlight upgrade, please have a look at my backlight page, especially the instruction sheet describing the upgrade process.

Good luck!

Jack Ng from the HPLX mailing list has written an excellent guide how to fix the screen rot problem which many HPLXs suffer from:

CLICK HERE