COMMODORE KEYBOARDS Troubleshooting and maintenance of C64 and C128 (including C128DCR) Latest updates and/or corrections: 11-17-2015 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 and A 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 can even 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 rubber 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 THE c64 KEYBOARD Cleaning the keypads and PC board will correct non-functioning keys -if the problem is dirt or other debris-. After removing the board (lots of tiny screws and one soldered switch) from the keyboard top, wipe the dust off the PC board with a clean cloth, if necessary. Don't rub or scratch the conductive spots on the board. They normally have a coating to prevent corrosion and oxidation of the copper underneath. If there is some corrosion that you must remove from a -copper- clad board, rub the spots -gently- with a pencil eraser, then clean the board with alcohol and wipe dry. Clean fingerprints from the board contact areas. Oil and moisture from your skin can cause problems. The contact areas should be shiny copper. NOTE: some boards (the SX for one) have black conductive paint over the contact areas rather than copper. Unless you encounter a liquid spill that needs to be cleaned off, it's best to leave those areas absolutely alone. If the black conductive coating is rubbed off, the board will become unserviceable!!! Blow any dust out with compressed air or vacuum, and remove any hair or fibers left behind from the Q-tip or cloth. The first and least invasive restoration attempt of the conductive rubber pads should be done by pulling a clean strip of paper across each one. The rubber pads are thin and flexible, so be careful you don't tear or dislodge them. With one hand, use a finger to hold each key down and press the paper gently against the pad with your thumb while pulling the paper across the pad with the other hand. You'll have to do one side of the board (two or three rows of keys) and then turn the board around and do the other rows. Don't touch the keypads with your fingers, but if you do accidentally, make sure you clean off the oil with alcohol or other solvent before reassembly. Never use abrasives on the board or keypads in an effort to clean them. It only makes matters worse and may render the entire board unserviceable. If contaminated from a spill, 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. 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 that 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 electrical conductivity (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 failing keypads or the entire plunger with pad attached. 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 ones most used 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 for another similar computer. Many parts are interchangeable between computers and all keys are the same inside. To make sure you have a good one to install, either measure it with an ohmmeter across the two protrusions of the pad, or just examine it closely. Worn pads will look shiny... good ones will have a dull looking surface. New pads will measure between 100 and 1000 ohms (1K ohms). When they start to require more pressure to make them work, the resistance of the pad will be up around 10K ohms or more. If the resistance is too high, the computer does not sense a keypress. 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 as can one with a missing spring under the keytop. You can see it if you examine the keyboard as it will be lower than the other keys. If one letter appears on the command line of the startup screen with a flashing cursor after it, or it starts printing a letter repeatedly on the screen at startup, 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 being held down (shorted contact on the PC board. Unplug any mice or 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. Beyond that, stuck keys or whole rows or columns that don't respond may be due to a failed CIA interface chip in the computer. If unplugging the keyboard doesn't resolve a "stuck key" symptom, that's another indication of a failing CIA. REMOVAL OF KEYTOPS Removal of the keytops must be done with great care so as not to damage the top or break the plunger underneath. The tops are a press fit onto the plungers that stick up through the plastic housing. A spring under each top makes the key come back up when not pressed. You might be tempted to use a knife or 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 may break the plunger, keytop shaft or both. Prying against another key will likely 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 or 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 over the keytop. ________ / \ | | | | | | | | | | | | | | |_ _| 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 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. If you have a broken keytop and no spare parts handy, the shaft can be glued back on with SuperGlue, but first you have to extract the broken stub from the plunger. Don't be tempted to just glue it back without removing the broken stub from the plunger! If you do, you'll never get that keytop off again, ever. Also, that glue tends to wick its way into other areas. So, you'll probably end up with a key that's stuck forever. Make the extra effort and extract the broken stub of the keytop shaft out of the plunger, I use a paperclip with one end bent into an L shape small enough to fit into the small hole in the shaft. Insert the tool into the hole and pull it out quickly. It may take several tries, but that trick usually works and doesn't damage anything. Now, orient the broken shaft bit over the bottom of the keytop so it sits straight. Note the position and prepare to glue it back on. To reinforce the mend, trim a wooden toothpick or the wooden shaft of a Q-tip to tightly fit the tiny hole in the shaft and the broken stub. Force it into the bottom of the keytop and then the broken shaft down over it until it fits snug. When you are satisfied it sits straight and is a good tight fit, remove the stub from the stick and apply the glue, then press the stub back over the stick. Immediately wipe away any excess of glue that is pressed out with a Q-tip. Let the repair set at least an hour before you try to use it. Trim off any wood sticking out of the hole if necessary. The repaired keytop should now work when pressed into place. A broken plunger (actually more common) is not usually repairable. If it's cracked along the side and the keytop will not stay on, no repair I've ever tried was reliable... it would break again or the mend was "sticky" in the hole. DISASSEMBLY / REASSEMBLY... C64 Computer 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 quickly 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 easily. 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 Computer The procedure is very similar to the C64, but the C128 has three keyswitches to unsolder. These switches are plastic and can melt from too much heat on their terminals... desolder them quickly! 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. The newer 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, desolder 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. I use tweezers to move the wires while the solder is molten. You can cut the wires but may not have enough to resolder them when it's time to reassemble the keyboard. There is no need to re-wrap them around the switch terminals when you solder them back on. "Tack" soldering is good enough... just let the wire touch the switch terminal and solder the two together. Remove the 27 tiny philips screws and lift up the PC board. Notice the tiny spring off to one side... don't lose it! It will fall out if you turn the panel over. That spring provides a ground connection between the metal frame of the keyboard and the PC board. It's there to discharge static electricity safely and harmlessly to chassis ground. You will not see any difference in normal operation without it, but leaving it out can open the computer CIA chips to possible damage from static electricity. Clean and replace parts as needed. The assembly is similar in design to the C64, but parts are not interchangeable between the two. Additional note: there are two versions of keyboards for the flat C128 but they look identical, and the PC board has the same CBM part number: 310401-01. The difference in the two versions is the length of the plungers under the keytops. In one version, green and white plungers are 3/8" long and in the other, blue and black plungers are 7/16". They are therefore not interchangeable. A longer plunger might fit and work as a replacement for a shorter one, but that keytop will stick up higher than all the others. Follow the previous instructions as far as parts 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 over 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 and don't overtighten any of the screws. The plastic can't take much torque before it strips out. DISASSEMBLY / REASSEMBLY... C128DCR COMPUTER KEYBOARD Unlike the keyboard in the C128, the 128DCR keyboard is inside of its 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. Those feet are held with double-sided tape and are easy to remove. I like to permanently remount them close to but not covering the access holes. That makes it easier the next time I need to open the case. Rather than "peel and stick" tape, I use Superglue to remount the rubber feet near the original spaces but not covering the screws again. As with the 128 keyboard, there are 27 tiny screws that hold the PC board to the assembly. The interconnect cable is soldered to the board and a plastic wire tie secures that cable to the board. The board can be opened and cleaned without cutting that tie. Before you disassemble the keyboard, it's a good idea to blow the dust and debris from the top. Lint and hair may be trapped under the keys, so if there is a lot of it that doesn't respond to blowing it out with an airhose, you may need to remove some of the keytops to get at it. If you do that before you remove the board, the plungers will not fall out when keytops & springs are removed. Wide keys such as the ENTER key have a wire clip that is rather difficult to put back correctly. Note how it comes off, and work carefully so you don't break the plastic retainers that hold the clip in place. If a keyboard is really gunked up, I remove the key assembly from the PC board and spray Windex all over the keytops, then wipe them with a soft paintbrush. That will loosen most of the dirt and gunk under the keys. A flush with hot water washes away all the debris. I shake the assembly to eliminate most of the water and set the assembly aside to dry. A small fan blowing on the assembly will speed drying. After that, I then rub each pad with a sheet of paper (see above) to "polish" the contacts. The keys are all part of an integrated metal and plastic subchassis, and if that main deck is damaged, it may not be repairable. However, most of the time failures are due to bad contacts, a broken plunger or a broken keytop. The plastic subchassis is mounted over a "motherboard" where each plungers conductive pad touches the corresponding board contacts when a key is pressed. Don't use abrasives or rub on the conductive surfaces when cleaning the PC board. Those contacts are just a carbon powder coating and are easily damaged. Use a mild cleaner such as Windex or rubbing alcohol on a cloth to clean up any spills on the board but -don't- rub hard. Wipe dust and debris off with a dry cloth or just use compressed air. The three keyswitches (Caps Lock, 40/80, & Shift Lock) wires connect to the board and must be unsoldered carefully (see instructions above). As with a C128 keyboard, all keypads wear out with use and then require increased pressure on the keys to make them work. If cleaning doesn't restore normal operation, replace the pad. If you don't have spares, swap the pad or the entire plunger with one from another key that isn't used as often. The pads just snap onto the bottom of the plunger but that requires removing the plunger from the subchassis. Note that plungers and springs under the keytops are interchangeable with some C128 keyboards (there are two versions of flat 128 keyboard, each with a different length plunger). Although they look identical, C128DCR keytops have a longer shaft to fit their plungers, so not all C128 keytops will work. DCR keytops may therefore fit some C128 keyboards. My DCR keyboard is a Mitsumi and uses the longer keytops. THE SX KEYBOARD: Because of the unique design of the SX-64 keyboard, I wrote a separate article for that computer hardware. Look in the SX directory for it. Ray Carlsen CET CARLSEN ELECTRONICS If you have questions or comments, or more importantly if you spot any mistakes here, please let me know. Thanks!