Keyboard Failure – Symptoms and Troubleshooting

Introduction

Keyboards are the classic input device. By manipulating a matrix of individual electrical switches, commands, and instructions can be entered into the computer one character at a time. If you’ve used computers or typewriters to any extent, you already have an excellent grasp of Keyboard handling. However, Keyboards are not without their share of drawbacks and limitations. Although today’s Keyboard switches are not mechanically complex, there are a number of important moving parts. When you multiply this number of moving parts times the 80 to 100+ keys on a typical Keyboard, you are faced with a substantial number of moving parts. A jam or failure in any one of these many mechanical parts results in a Keyboard problem. Most Keyboard failures are hardly catastrophic, but they can certainly be inconvenient. This chapter gives you the information needed to understand and repair computer Keyboards.

Keyboard Cleaning and Maintenance

Keyboards are perhaps the most abused part of any computer, yet they are often ignored until serious problems develop. With some regular cleaning and maintenance, however, a Keyboard can easily last for the lifetime of a computer. This part of the chapter shows you some practical techniques for Keyboard service.

Correcting Problem Keyboards

Virtually all computer Keyboards are open to the air. Over time, everyday dust, pet hair, air vapor, cigar/cigarette smoke, and debris from hands and ordinary use will settle into the Keyboard. Eventually, accumulations of this foreign matter will cause keys to stick, or will prevent keys from making proper contact (i.e., a key does not work every time it is pressed).

In either case, Keyboard problems will develop. Fortunately, correcting a finicky Keyboard is a relatively straightforward process. Start by removing the key caps of the offending keys. Be sure to note where each key is placed before starting your disassembly especially if the Keyboard is a DVORAK-type or unusual ergonomic design. To remove a key cap, bend an ordinary paper clip into the shape of a narrow “U”, and bend-in small tabs at the tip of the “U” shape. Slip the small tabs under the key cap and pull up gently. Do not struggle with the key cap. If a cap will not come off, remove one or more adjacent caps. If there is a substantial accumulation of foreign matter in the Keyboard, you should consider removing all of the key caps for a thorough cleaning, but this requires more time

Flip the Keyboard upside down and rap gently on the case. This will loosen and dislodge any larger, heavier foreign matter, and allow it to fall out of the Keyboard. A soft-bristled brush will help loosen the debris. Return the Keyboard to an upright position. Use a can of compressed air (available from almost any electronics or photography store) to blow out the remainder of foreign matter. Because this tends to blow dust and debris in all directions, you might wish to use the compressed air outside or in an area away from your workbench. A medium- or firm-bristled brush will help loosen any stubborn debris.

Now that the Keyboard is cleaned out, squirt a small amount of good-quality electronicsgrade contact cleaner (also available from almost any electronics store) into each key contact, and work the key to distribute the cleaner evenly. Allow a few minutes for the contact cleaner to dry completely and test the Keyboard again before reinstalling the key caps. If the problems persist, the Keyboard might be damaged or the individual key(s) might simply be worn out beyond recovery. In such an event, replace the Keyboard outright.

Vacuum Cleaners And Keyboards

There is an ongoing debate as to the safety of vacuum cleaners with computer equipment. The problem is static discharge. Many vacuum cleaners—especially small, inexpensive models—use cheap plastic and synthetic fabrics in their construction. When a fast air flow passes over those materials, a static charge is developed (just like combing your hair with a plastic comb). If the charged vacuum touches the Keyboard, a static discharge might have enough potential to damage the Keyboard-controller IC, or even travel back into the motherboard for more serious damage.

670 Keyboards

Avoid removing the <Space Bar> unless it is absolutely necessary because the space bar is often much more difficult to replace than ordinary keys. If you do choose to use a vacuum for Keyboard cleaning, take these two steps to prevent damage. First, be sure that the computer is powered down and disconnect the Keyboard from the computer before starting service. If a static discharge does occur, the most that would be damaged is the Keyboard itself. Second, use a vacuum cleaner that is made for electronics work and certified as “static-safe.” Third, try working on an anti-static mat (such as the mat in Fig. 20-7), which is properly grounded. This will tend to “bleed-off” static charges before they can enter the Keyboard or PC.

Replacing The <Space Bar>

Of all the keys on the Keyboard, replacing the <Space Bar> is probably the most difficult. The <Space Bar> is kept even by a metal wire that is inserted into slots on each leg of the plastic bar key. However, you have to get the wire into the slots without pressing the wire.

If you push the wire down, you compress the wire and installation becomes impossible.

As a general rule, do not remove the <Space Bar> unless absolutely necessary. If you must remove the <Space Bar>, remove several surrounding key caps also. This will let you get some tools under the <Space Bar> wire later on. Once the <Space Bar> is re-inserted, you can easily replace any of the other key caps.

Preventing The Problems

Keyboard problems do not happen suddenly (unless the Keyboard is dropped or physically abused). The accumulation of dust and debris is a slow process that can take months (sometimes years) to produce serious, repetitive Keyboard problems. By following a regimen of regular cleaning, you can stop problems before they manifest themselves in your Keyboard. In normal office environments, Keyboards should be cleaned once every four months. Keyboards in home environments should be cleaned every two months. Keyboards in harsh or industrial environments should be cleaned even more frequently.

Turn your Keyboard upside-down and use a soft-bristled brush to clean between the keys. This prevents debris that might already be on the keys from entering the Keyboard. Next, run the long, thin nozzle of your compressed air can between the key spaces to blow

Keyboard Cleaning And Maintenance 671

A Curtis

Anti-Static Keyboard Mat. Curtis, a division of Rolodex, Secaucus, NJ 07094 out any accumulations of dust. Because compressed air will tend to blow dust in all directions, you might consider “blowing down” the Keyboard outside, or in an area away from your workbench. Instead of compressed air, you might use a “static-safe” vacuum cleaner to remove dust and debris.

Dealing With Large Objects

Staples and paper clips pose a clear and present danger to Keyboards. Although the odds of a staple or paper clip finding its way into a Keyboard are generally slight, foreign objects can jam the key or short it out. If the Keyboard is moved, the object can wind up in the Keyboard’s circuitry where serious damage can occur. When a foreign object falls into the Keyboard, do not move the Keyboard. Power down the PC, then locate the object and find the nearest key. Use a paper clip bent in a “U” shape with the ends of the “U” angled inward to remove the nearest key cap. Use a pair of non-conductive tweezers or needle nose pliers to remove the object. Replace the key cap.

Dealing With Spills

Accidental spills are probably the most serious and dangerous Keyboard problem. Coffee, soda pop, and even tap water is highly conductive (even corrosive). Your Keyboard will almost certainly short circuit. Immediately shut down your computer (you might be able to exit your application using a mouse) and disconnect the Keyboard. The popular tactic is to simply let the liquid dry. The problem with this tactic is that most liquids contain minerals and materials that are corrosive to metals—your Keyboard will never be the same unless the offending liquid is removed before it dries. Also, liquids tend to turn any dust and smoke film into a sticky glue that will just jam the keys when dry (not even considering the sticky sugar in most soda pop).

Disassemble the Keyboard’s main housings and remove the Keyboard printed-circuit assembly. As quickly as you can after the incident, rinse the assembly thoroughly in clean, room-temperature, de-mineralized water (available from any pharmacy for contact lens maintenance). You can clean the plastic housings separately. Do not use tap water. Let the assembly drip dry in air. Do not attempt to accelerate the drying process with a hair dryer or other such heat source. The de-mineralized water should dry clean without mineral deposits or any sticky, conductive residue. Once the assembly is dry, you might wish to squirt a small amount of good-quality, electronics-grade contact cleaner into each key switch to ensure that no residue is on the contacts. Assuming that the Keyboard’s circuitry was not damaged by the initial spill, you should be able to reassemble the Keyboard and continue using it without problems. If the Keyboard behaves erratically (or not at all), replace the Keyboard outright.

Disabling A Keyboard

Keyboards are an essential peripheral for all computers, except servers. In many cases, network administrators would prefer to restrict direct access to the server, and prevent potential tampering. Traditional PCs did not allow you disable the Keyboard, but newer systems do offer a CMOS setup entry that can enable or disable the Keyboard. When the Keyboard is disabled through CMOS, the PC will boot without suffering “Keyboard not found” errors. Before starting service on a server, it might be necessary to reattach and reenable the Keyboard.

Keyboard Troubleshooting

Although their appearance might seem daunting at first glance, Keyboard systems are not terribly difficult to troubleshoot. This ease is primarily because of the Keyboard’s modularity— if all else fails, it’s a simple matter to replace a Keyboard outright. The Keyboard’s great weakness, however, is its vulnerability to the elements. Spills, dust, and any other foreign matter that finds its way between the key caps can easily ruin a Keyboard. The Keyboard’s PC board is also a likely candidate to be damaged by impacts or other physical abuse. The following procedures address many of the most troublesome Keyboard problems.

Symptom 20-1. During initialization, an error message indicates that no Keyboard is connected Check your Keyboard cable and see that it is inserted properly and completely into the PC connector. Remember that you will have to reboot your system to clear this error message. Try another compatible Keyboard. If a new Keyboard assembly works properly, there is probably a wiring fault in the original Keyboard. Given the very low price of new Keyboards, it is usually most economical to simply replace a defective Keyboard. If you’re working on a file or network server, see that the CMOS setup has enabled the Keyboard.

If a known-good Keyboard fails to function, try the original Keyboard on a known-good PC to verify that the Keyboard itself is indeed operational. If so, your trouble now lies in the PC. Check the wiring between the PC Keyboard connector and the motherboard. Check the connector pins to be sure that none of them have been bent or pushed in (resulting in a bad connection).

You might also want to check the soldering connections where the Keyboard connector attaches to the motherboard. Repeated removals and insertions of the Keyboard might have fatigued the solder joints. Reheat any defective solder joints. If the Keyboard connector is intact, it is likely that the Keyboard controller IC (KBC) has failed. Try booting the PC with a POST board installed (as covered in Chapter 15). A KBC failure will usually be indicated by the system stopping on the appropriate POST code. You can attempt to replace the KBC or replace the motherboard outright. If a POST board indicates a fault other than a KBC (such as the programmable interrupt controller, which manages the KBC’s interrupt), you can attempt to replace that component, or simply exchange the motherboard anyway.

Symptom 20-2. During initialization, an error message indicates that the Keyboard lock is on In many cases, the detection of a locked Keyboard will halt system initialization. Be sure that the Keyboard lock switch is set completely to the “unlocked” position. If the switch is unlocked, but the system detects it as locked. The switch might be defective. Turn off and unplug the system, then use a multimeter to measure continuity across the lock switch (you might need to disconnect the lock switch cable from the motherboard. In one position, the switch should measure as an open circuit. In the opposing position, the switch should measure as a short circuit. If this is not the case, the lock switch is probably bad and should be replaced. If the switch measures properly, there is probably a logic fault on the motherboard (perhaps the Keyboard controller). Your best course is to try another motherboard.

SYSTEM DATA AND TROUBLESHOOTING

Symptom 20-3. The Keyboard is completely dead—no keys appear to function at all other computer operations are normal. In this symptom, it is assumed that your computer initializes and boots to its DOS prompt or other operating system as expected, but the Keyboard does not respond when touched. Keyboard-status LEDs might not be working properly. Your first step in such a situation is to try a known-good Keyboard in the system. Notice that you should reboot the system when a Keyboard is replaced.

If a known-good Keyboard works, the fault is probably on the Keyboard-interface IC. You can attempt to replace this IC if you wish, but it is often most economical to simply replace the Keyboard outright.

If another Keyboard fails to correct the problem, use a multimeter and check the +5-V supply at the Keyboard connector (refer to Fig. 20-5). If the +5-V signal is missing, the female connector might be broken. Check the connector’s soldering junctions on the motherboard. Reheat any connectors that appear fatigued or intermittent. Many motherboards also use a “pico-fuse” to protect the +5-V supply feeding the Keyboard connector.

If your +5 V is lost, locate and check the Keyboard-connector fuse. If problems continue, replace the motherboard.

Symptom 20-4. The Keyboard is acting erratically One or more keys appear to work intermittently, or it is inoperative. The computer operates normally and most keys work just fine, but one or more keys do not respond when pressed. Extra force or repeated strike might be needed to operate the key. This type of problem can usually range from a minor nuisance to a major headache. Chances are that your key contacts are dirty. Sooner or later, dust and debris works into all key switches. Electrical contacts eventually become coated and fail to make contact reliably. This symptom is typical of older Keyboards, or Keyboards that have been in service for prolonged periods of time. In many cases, you need only vacuum the Keyboard and clean the suspect contacts with a good-quality electronic contact cleaner.

Begin by disconnecting the Keyboard. Use a static-safe, fine-tipped vacuum to remove any accumulations of dust or debris that might have accumulated on the Keyboard PC board. You might wish to vacuum your Keyboard regularly as preventive maintenance.

Once the Keyboard is clean, gently remove the plastic key cap from the offending key(s). The use of a keycap-removal tool is highly recommended, but you might also use a modified set of blunt-ended tweezers with their flat ends (just the tips) bent inward. Grasp the key cap and pull up evenly. You can expect the cap to slide off with little resistance. Do not rip the key cap off—you stand a good chance of marring the cap and causing permanent key switch damage.

Use a can of good-quality electronics-grade contact cleaner and spray a little bit of cleaner into the switch assembly. When spraying, attach the long, narrow tube to the spray nozzle—this directs cleaner into the switch. Work the switch in and out to distribute the cleaner. Repeat this maintenance once or twice to clean the switch thoroughly. Allow residual cleaner to dry thoroughly before re-testing the Keyboard. Never use harsh cleaners or solvents. Industrial-strength chemicals can easily ruin plastic components and housings.

Reapply power and retest the system. If the suspect key(s) respond normally again, install the removed key caps and return the system to service. As a preventive measure, you might wish to go through the process of cleaning every key.

Membrane keys must be cleaned somewhat differently from mechanical keys. It is necessary for you to remove the rubber or plastic boot to clean the PC board contacts. Depending on the design of your particular membrane switch, this might not be an easy task. If you are