In the process of owning and operating an IBM PC, you will, no doubt, find a point in time that the keyboard causes strange and irritating things to happen to your fond finger strokes. Nine times out of ten, this is caused by DIRT! It is amazing how much trash can be found under the keytops of any keyboard that has been in use for more than a few weeks. Human hands carry a great deal of trash, including dead skin cells. In addition, leaning over a keyboard, as computer people are prone to do, can cause much "head garbage" to fall into the mechanism. If you smoke (as I do), you'll find it next to impossible to keep ashes in the ashtray. The symptoms of a keyboard dirt problem are manifold, but the most common are: mistyped characters, missing letters (Did I miss the key?), and having the wrong character appear at the most obnoxious times. The fix to most of these problems is to clean the bugger out. To do this you must remove the keytops and blow out the mechanism with air. The purpose of this message is to explain the operation of the PC keyboard and to outline the steps necessary to clean it. I've included some notes on some possible pitfalls that a few folks have run into. The PC keyboard is a capacitive device, that is, its internal circuitry detects each keystroke by a change in the capacitive potential of a wire matrix the keys are mounted on. This matrix is contained in the form of a circuit board that contains small "plates" that connect to a device that monitors capacitive levels. Above each of these plates is a "toggle" made of conductive plastic (like they ship IC's in). The toggles are connected to a small spring that is held straight and slightly compressed in a small cylinder. The thing that hold the spring compress is a small plunger attached to the bottom of each key. When the toggle moves in its holder, it changes the capacitive potential of the wire matrix and causes the keyboard logic circuits to send a scan code to the 8088 bus. When you press a key, the plunger moves down in the cylinder, compressing the spring. This spring is already holding the toggle away from the matrix. As the pressure increases, the spring becomes "unstable" and bends rapidly to form a loose "U" shape. This action is felt (and heard) as the "break" of the key. When the key breaks, the direction of the pressure on the toggle is reversed, causing it to swing down about 1.5mm closer to the matrix. This is detected by the keyboard logic circuitry as a change in capacitive potential and the appropriate scan code is sent to the 8088 bus, to be processed. When you lift your finger from the key, the spring pops back to its straight position and lifts the toggle away from the matrix. As you can see, there is alot of mechanical interaction going on inside of the lowly keyboard. What amazes me is that the devices are as reliable as they are! To clean the keyboard, turn off the PC and place the keyboard in you lap. Remove each key by prying it STRAIGHT UP with a penknife of small screwdriver until it pops off. Check each key for any gummy or sticky matter, placing the dirty keys in a pile to be cleaned with soap and water. DO NOT REMOVE THE SPACE BAR!!! If you do, youll find it is almost impossible to replace properly. After removing the keys, take a low- pressure air hose (or hair dryer) and blow a stream of air down into the key tubes. The air will remove quite a bit of loose dirt from the inside of the keyboard. This dirt, if left in place, will alter the capacitive potential of the matrix, thus "fooling" the keyboard circuitry into thinking a key has been pressed when it has not. A WORD OF WARNING: Do NOT-NOT-NOT blow into the key tubes with your mouth!!! You will blow moisture into the mechanism, and possibly ruin the keyboard unit ($125.00 spare part). Nine times out of ten, all that is necessary to correct keyboard errors is to clean the keys, and the rest of this is not required. If you did not heed my warning about the mouth air, you will have to remove the matrix board from the key tube holder and clean it. THIS IS A VERY DELICATE OPERATION! DO NOT-NOT-NOT ATTEMPT IT UNLESS YOU NEED TO! To remove the key matrix, turn the keyboard over and remove the two screws on the bottom. Remove the bottom panel from the keyboard and disconnect the Berg connector that holds the keyboard cable to the circuit board inside the unit. Place the keyboard in your lap and remove ALL the keys. Carefully turn the unit upside-down, taking care not to bend the springs. With the keyboard upside-down, and the PC (printed circuit) board on the right side, you will see several metal "clips" holding the silver matrix board to the black key tube holder. One of these clips (probably on the lower left) is bent over the silver matrix holder. Bend this clip away from the silver metal. Hold the two parts together FIRMLY and slide the silver matrix holder to the right (on mine, at least). THIS TAKES ALOT OF PRESSURE! BE SURE YOU DON'T ALLOW THE TWO PARTS TO SEPARATE SUDDENLY, OR YOUR FLOOR WILL BE LITTERED WITH TOGGLES. Carefully remove the matrix holder from the tube holder and place the tube holder in a safe place. Use a clean, slightly damp rag to clean the surface of the matrix board. DO NOT ALLOW WATER TO GET UNDER THE BOARD! Allow the unit to dry. You may perform an interesting test by reconnecting the matrix board to the cable and powering-up the computer. You may then "type" on the matrix board by touching your fingers to the dark panels visible under the surface of the board. Cute, huh? You will need to practice reassembling the space bar spring before you try to put the unit back together. To do this, remove the spacebar tubes from the tube holder. Remove the toggle and place it in a safe place. Note the wire running the full length of the space bar tube assembly. This wire is the spring that keeps the spacebar from tilting to one side during use. When the spacebar is inserted into the tube assembly this wire MUST fit into the slots in the "legs" on each end of the spacebar. Try it a few times before you plan to reassemble the keyboard. To reassemble the keyboard, replace the spacebar tube assembly in the tube holder. Install the toggle in its slot. Insure all other toggles are correctly positioned. Hold the tube holder upside down and GENTLY replace the matrix board in its place. To complete reassembly, you will need to press the matrix holder down onto the tube holder while sliding the "ears" into their correct notches. THIS TAKE A LARGE AMOUNT OF FORCE! BE SURE THE UNIT DOES NOT JUMP OUT OF YOU HAND!!! After replacing the matrix board, bend the holding "ear" into place to secure the mechanism. Reinstall the key unit into the keyboard case and reconnect the cable. Replace the bottom cover. You should now check the unit for proper operation. This is tricky without keys, but it can be done. To test the unit, place the rear edge (nearest the number keys) on the table with the front edge (nearest the spacebar) in the air. This will allow the springs to fall backwards and insure against false input signals. You may have to shake the keyboard a bit to get the springs to fall. Bring the system up and test each key by "tweeking" the spring with your finger. (The IBM diagnostics have a good test for this.) If all is well, replace the keys, WHILE HOLDING THE KEYBOARD IN THIS POSITION! If you don't hold the keyboard up like this, the springs will be "pre-bent" and won't function properly. Replace the spacebar first, as this is the one that is most likely to give you problems. The object of the spacebar replacement game is to get the wire into the slot on the bar legs. This MUST be done one side at a time, without depressing the bar too much. Pressing the bar down causes the wire springs to retract and makes their reinstallation impossible. You can tell the spacebar is installed correctly by the fact that the ends are difficult to lift up and the bar moves vertically as a unit. After replacing the spacebar, replace all the other keys, WHILE HOLDING THE KEYBOARD VERTICAL! Run the diagnostics of the keyboard to insure everything is working properly. If not, check that the small springs were in the correct (leaned- back) position when the keys were installed. If they were and you still have problems, then you reassembled the matrix board and key tube holder incorrectly and will have to take it apart and start all over again... A common problem is getting the toggles jammed up when installing the matrix board. Hope this was educational -- it sure was a pain to type! GOOD LUCK! David R. Bivens Richmond, Va. Code: source:- http://www.textfiles.com/computers/cleankey.txt Now my tit-bits; In the above tut it is said that you can remove the keys from the socket and clean the surface below it. It is true and I have tested it on my MS Basic keyboard. But here are some of the tit bits I wanted to add that I faced when I was cleaning my keyboard. When removing the buttons: 1. Don't be in a hurry, be patient and see that you have lots of time coz this cleaning thing takes a lot of time believe me (1 keyboard taked 2 hrs of cleaning). 2. When removing the keys use a non sharp but hard screwdriver. You can use the T-shaped magnetic screwdriver (that's what I used) but heres the catch don't use much of pressure coz it will break the keys, or the keys will get cuts (if u want to know what cuts are just take some plastic waste thing and write on it with the sharp corner of the screwdriver, believe me it looks awful), now cuts dont look nice so we can avoid them by using a rubber padding or a cloth between the screwdriver and the keys. 3. When removing the keys insert the screwdriver between the gap of the key and then slowly raise one side of the screwdriver. Now while doing this always keep 1 finger on the keytop and ensure that the key is straight coz if the key becomes inclined one side of the key will break, and believe me u dont want that to happen. And the finger is just to ensure that the key is straight do not press the key hard. 4. The space key is a pain in the a$$ so pls if ur not sure dont remove it. I spent 10 mins figuring out how to remove it properly and I succeded anyways if u cant dont remove it coz we need spacebar so much. 5. After removing all the keys take the keybd to an open place blow the dirt away (dont use the suction thingy in a vaccum), u might also use a normal brush to brush the dirt away. Then use the blower. I also wiped the sorface of my keybd. But it was a real pain man it took a long time but it was worth it. 6. This tut doesnt apply to multimedia keybds which have multimedia buttons which dont look like the normal keybd buttons. They cant be cleaned so leave them. 7. Although the above tut says that its ok to open the keyboard still u dont do it I lost 1 hr of my studies when I had opened one of my colleges keyboard so my advice dont try it. 8. Wierd tip: - Just my fantasy take a thin strip of paper and sprat it with perfume and insert it in between the keys and the keyboard will smell nice.