COMMODORE KEYBOARDS... Troubleshooting and maintenance Sooner or later with use, computer keyboards show their age. The most common "first sign" of a problem: some frequently used keys require more force to make them work, or they don't work at all. The Shift keys, Spacebar, and commonly used letters such as E are the first to show symptoms. To anyone who is proficient at the keyboard, it quickly becomes intolerable to have to stop and restrike a key that didn't work the first time. The most common way to overcome the problem, at least temporarily, is to strike the keys with more force. Very soon after, even that becomes useless... the keys do not respond no matter how much force is used, and the keyboard needs to be repaired. Other keyboard problems take a bit of detective work to diagnose and solve. The design of a Commodore keyboard is simple and elegant. It works well and lasts a long time. When keys do become unresponsive, it can be from several causes. If only one or two are not working (or require a lot of force to make them work), it's usually because those internal keypads are worn or dirty. Sometimes dirt can work it's way into the internals of a keyboard. A bit of dirt, hair or a liquid spill can render the key(s) inoperative if such debris gets between the conductive rubber keypad and the underlying PC board. If many keys are not working (a whole row, for example), the cause is normally either a failing CIA (keyboard interface) chip in the computer, or a bad connection between the keyboard and the motherboard. No problem with the keyboard itself will -prevent- the computer from displaying the startup screen, by the way. The keyboard could be unplugged from the motherboard for diagnostic purposes, and the computer will still display the opening screen. Electronically, pressing a key connects a matrix "row" (one of eight) with a "column" (one of eight) and provides "keyscan" data input to a chip called a CIA (Complex Interface Array). The coded 8 bit data output of that chip tells the microprocessor which key was pressed. Some of those keyboard data lines are "shared" with the joystick inputs. One key that doesn't go to the CIA is the RESTORE key. It simply grounds an input line to a timer chip. Two more inputs in a C128: the 40/80 switch, and the Caps Lock switch are likewise not part of the rows/columns inputs. IF YOU MUST PRESS HARD TO MAKE KEYS WORK Fortunately, most keyboard problems are of the "I have to step on this key to make it work" variety. Commodore keyboards are easy to pull apart and clean. That is sometimes all that's needed to make them work again. At worst, the little rubber keypads deteriorate and must be replaced, either with new ones or swapped with ones from seldom used keys. The pads are attached to "plungers" under each keytop... normally the plunger (with keypad attached) is swapped out as a unit, but you could remove just the pad... it comes off the plunger easily. Very worn pads will look "shiny". If failing because they have been used a lot, unresponsive key pads don't benefit much (if at all) from cleaning... they must be replaced. CLEANING Cleaning the keypads and PC board will correct non-functioning keys -if the problem is dirt or other debris-. After removing it from the keyboard top, wipe the PC board with isopropyl alcohol (rubbing alcohol works fine) and dry with a clean cloth. Don't rub or scratch the conductive spots on the PC board. They normally have a coating to prevent corrosion and oxidation of the copper underneath. If there is some corrosion that you must remove, rub the spots -gently- with a pencil eraser, then clean the board with alcohol and wipe dry. If bare copper is exposed, it will oxidize, and the repair will not last. It's best to avoid rubbing those conductive traces. Clean any fingerprints from the board. Oil from your skin can cause problems later. The rubber keypads can be cleaned with alcohol on a Q-tip. It's best not to spray anything inside the keyboard. The spray goes everywhere and just attracts dirt. To wipe off any residue from cleaners, lightly rub a clean sheet of paper over each key pad while pressing the key. The rubber is thin and flexible, so use care so as not to tear or dislodge it. Clean only the pads that need it... leave the others alone. Blow any dust out with compressed air, and remove any hair or fibers left behind from Q- tip or cloth. Don't touch the keypads with your fingers, but if you do accidently, make sure you clean off the oil with alcohol or other solvent before reassembly. CLEANING VS REPLACEMENT I did some experiments with good and bad keypads. I tried various kinds of cleaners including solvents, and rubbing with paper and emory cloth. After all this, I have come to the conclusion that for a key worn out by normal use, cleaning is useless. The conductive rubber itself deterioriates and cannot be "rejuvinated". A new key will measure less than 1000 ohms (1K ohm) across the two ends of the rubber keypad. If used a lot and starting to fail, it will measure more than 10K ohms. At that point, the user will notice that it takes a lot of force to make the key work. Nothing I tried would make a bad key better (unless the problem was dirt or contamination of the PC board), and interestingly enough, nothing I could do (including sandpaper and solvents) would increase the resistance (and therefore the pressure needed for proper key response by the user) of a good key. The good ones stayed good and the bad ones stayed bad, no matter what I did. So, with that in mind, if cleaning doesn't help (or you don't want to have to open the box again), just replace or swap out failing keypads. REPLACEMENT OF KEYPADS The quickest way to repair a keyboard if you have no spare parts on hand is to swap heavily used keys for ones not often used. The Shift keys, Spacebar, and letter keys like E and A for example, represent often used keys by the average user. Such keys as the Up Arrow, Back Arrow and pound key could be used as a "source of parts" for a quick keyswap. If you have an old C64 or VIC20 laying around, it could be used as a parts source... parts are interchangeable between those computers and all keys are the same inside. To make sure you have a good one to install, either measure it with an ohmmeter, or just examine it closely. Worn pads will look shiny... good ones will have a dull looking surface. The keyboards of the 128 and 128D appear to use the same parts inside, so interchange between those two should be possible (but I've never done it). STUCK KEY SYMPTOMS A stuck key can produce some rather confusing symptoms, depending on which key is stuck down. If the keyboard has ever suffered a liquid spill, one or more keys can get "sticky" from days to months later. Of course a broken key can stick down. If one letter appears on the command line of the startup screen with a flashing cursor after it, suspect that key of being stuck down. If the key feels OK, there might be some debris on the underlying PC board that simulates a key held down. Unplug the joystick(s) if used and try it again. If suddenly none (or only a few) of the keys work, check to see that none are stuck. Press each one and see if the "feel" of the key is right. A sticky one will not come back up like the others. A missing spring under a keytop can produce intermittant or "stuck key" symptoms. That's usually easy to spot just by looking. REMOVAL OF KEYTOPS Removal of the keytops must be done with great care so as not to damage the top or break off the plunger underneath. The tops are a press fit onto the plungers that go through the plastic housing. A spring under each top makes the key come back up when not pressed. Most people will use a screwdriver to remove a keytop, but that's not a good idea. The top must be pulled -straight- up and off. If you twist or bend it to one side, you will break the plunger. Prying against another key will mar or scratch it. You can make a simple tool that will pop those keytops off easily. Here's how to do it: With a pair of tin snips (metal shears) cut a strip of metal from a tin can (I used the top cut out of a dog food can) about 2 1/2 to 3" long and about 1/2" wide. Bend the ends over at a right angle with pliers to form a tiny lip (1/32" or less) at each end of the strip. Bend the strip into a U shape that fits over the keytop. The tool should be big enough so your finger will fit inside. ________ / \ i i i i i i i i [_ _] The lip at each end must be small enough so the tool will fit between keys, but large enough to grab the underside of the keytop. Note: the cut ends of the tin strip are very sharp! Wrap tape around the strip if necessary for protection. Now, press the tool over the keytop and, squeezing the sides gently to hold it in place, pull up on the tool and the keytop will come off easily. When it pops off, don't lose the spring underneath. Don't remove more than a few tops at a time unless you know where they go back. It's easy to get confused with keys that are not often used. (Ask me how I know.) It's best to have the PC board in place (held in place by a few screws, if necessary) so the plungers don't fall out when the keytops are removed. Plungers are removed from the bottom of the assembly. DISASSEMBLY / REASSEMBLY... C64 Remove three philips screws along the underside of the front edge of the computer. Lift up the top half-shell and unplug the keyboard and power indicator connectors. The keyboard connector may be hard to remove. Grasp the ends and gently rock it back and forth slightly while pulling straight up on it. Don't pull on the wires! Note that there is a blank pin on one end. That makes it difficult (but not impossible) to put the plug in backwards. The power LED connector will go either way... it doesn't matter, because it will work either way. The top half-shell can then be removed from the lower half. The rear fasteners are sometimes very tight and will "pop" when the top is folded back. That's normal. Rest the top (keyboard) face down on a cloth or cushion to keep from scratching the keys. Unsolder the ShiftLock switch wires: heat the connection and just pull the wire out when the solder melts. Remove 23 tiny philips screws holding the PC board to the keyboard assembly. The assembly need not be removed from the cabinet top, by the way. Lift the PC board up and out. Examine it for dirt or liquid spill residue, and inspect the rubber keypads for contamination or wear. Clean or replace pads as necessary. To remove a keypad, the keytop must be removed. (See REMOVAL OF KEYTOPS). With the keytop removed, the spring and plunger (with rubber keypad attached) will fall out. Make sure you don't lose anything! The plunger should slide out from underneath eas ily. If it doesn't, look for residue or cracks in the plastic. If it's broken or worn out, the plunger/keypad must be replaced. A plunger will fit in any slot... they are all the same. When installing a new plunger, don't forget the spring under the keytop. Temporarily install the PC board when you're ready to press the keytop back on. It gives the plunger something to push against, since you must apply pressure to the keytop to get it to "snap" back on. Don't use your finger to hold the keypad... oil from your fingers will contaminate the pad. When you're finished cleaning/repairing the assembly, reinstall the PC board and put the tiny screws back in. Don't forget to resolder the wires to the ShiftLock switch: heat the connection and poke the wire in when the solder melts. Plug the keyboard back into the motherboard, and plug the LED connector back in. Lay the back of the two half-shells together and fold the top back down. It helps to squeeze the cabinet together at the rear to seat the fasteners. Put the three screws back in the cabinet and you're done. DISASSEMBLY / REASSEMBLY... C128 and 128D The procedure is very similar to the C64, but the C128 (and the 128D) has three keyswitches to unsolder. These switches are plastic and can melt from too much heat... solder quickly! Of course the 128D keyboard is inside of it's own housing. It only requires the removal of six philips screws to get to the internals, but the screws are hidden beneath the rubber "feet" on the bottom of the keyboard. The feet are just "peel and stick" and so are easy to remove. I like to permanently remount them close to but not covering the access holes... makes it easier next time I need to open the case. On the "flat" 128: remove six screws (standard philips or Torx) from the bottom of the 128 case. Note: the 128 may have special screws holding the cabinet together. This new star-shaped type is call Torx. The screws require a special T-10 size driver to remove them, but a small flat blade screwdriver can be used if you're careful... just make sure it fits tightly in the screwhead. Lift the top half-shell, starting at the front edges. Two small plastic "snaps" hold the case together on each side, and so may make it difficult until you press in slightly on both sides near the top row of keys on each side to pop it open. With the top shell loose, lift up on the left side of the top shell, reach under and remove the power LED plug from the motherboard. Now grasp the top half with both hands and shift it to the left to expose the wiring (still connected) between the top and bottom shells. You need to remove the keyboard connnector and a small philips screw. The keyboard plug is usually very difficult to remove. Because it is recessed, you can't get enough of a grip on it to remove it with your fingers. Instead, grasp -all- of the wires tightly between thumb and forefinger (as close to the plug as you can) and pull up, gently rocking back and forth to loosen the plug from the socket. Next, disconnect the ground strap held to the motherboard on the right hand side with a small philips screw. You can now remove the top half-shell and set it face down on a cloth or padded surface. Unsolder the wires to the three keyswitches. They are plastic and will melt if the soldering iron is held on them too long, so solder quickly! The easiest way is to get under each connected wire and when the solder melts, lift the wire -gently- with the iron. If it's wrapped too tightly, you will need to unwrap it from the switch while the solder is molten. All I can say is: work quickly and carefully. A small screwdriver or tweezers is sometimes helpful to move the wires... don't burn your fingers. Removce the 27 tiny philips screws and remove the PC board. Clean and replace parts as needed. The assembly is similar in design to the C64, but parts are not interchangeable between the two. Otherwise, follow the previous instructions as far as part s replacement and cleaning. Reassemble in reverse order of disassembly. The keyboard connector will only go back one way. Be gentle. It's possible to bend pins if you're not careful. The power LED plug will fit and will work either way. Don't forget the ground shield at the right side of the motherboard. Don't overtighten any of the screws. The plastic can't take much torque before it strips out. If you have questions (or spot any mistakes here), please email me.