Tuesday, March 3, 2015

PC Keyboards I Have Known

IBM PC (Model 5150) Keyboard

While not the first keyboard I have ever used, the original 83-key IBM PC Model F keyboard is easily the most sturdy and well-constructed keyboard I have ever used.  Unlike the Model M, the 83-key uses a printed circuit board on which the keyboard traces are printed.  This circuit board is sandwiched between two pieces of steel.  The keyboard controller and circuitry is located at the top of the circuit board.

The 83-key keyboard can be completely separated and put back together though the use of steel tabs.  It is not something I advise, because once the back metal plate is removed, the key plates will go out of their places.  It is very tedious putting 83 of them back in their places, and the spacebar plate is especially tough to put back in place.  The top steel plate can show corrosion from any water or ill-usage.

The keys are easy to remove.  You can pop them out with a small, flat stiff object.  Once exposed, you will see the springs.  These should be treated with care, because if they get bent out of shape, the key will no longer work correctly.  The springs of a Model F may not be replaceable by those from a Model M.

The springs in the keys are stiffer than Model M springs and require more force to register a keystroke.  The spacebar is huge and also requires a lot more force to register its press.  The keyboard is extremely heavy but does have angle adjusting feet.  The feet require a good deal of strength to move their position.  It also has four cork pads to lie on and the keyboard can be disassembled with a slotted screwdriver.  The cork pads can fall off over time.

The PC Model F keyboard is not compatible with modern PCs, even with a 5-pin DIN to a 6-pin mini-DIN adapter. It is compatible with the IBM PC/XT, Tandy 1000 TL, SL and (with adapter) RL.  The IBM PC Portable uses the same keyboard but a different type of cable.

When you see the layout of the 83-key Model F, you can understand certain early conventions.  *.* makes perfect sense when you see the . and an * key where only two keys separate them.  Users of the IBM PC AT 84-key Model F keyboard lost out, because their . and * keys are not in a straight line horizontally or vertically from each other.  IBM rectified this in the Model M keyboard, the * key is three keys above the . key on the numberpad.  Ctrl Alt Del also made a great deal of sense when the keys were in an L shape.  Finally, when certain games use F1 as a fire key, it makes sense when the function keys are on one side of the keyboard and the directional keys are on the other side.

Even so, this keyboard is very difficult to get used to after using the standard 101/104 Windows key layout.  Ctrl is not in the place where you would expect, the shift keys are way too small and the vertical enter bar is difficult to hit.  The inverted T for the arrow keys is solely missed.

IBM Model M Keyboard

I have three Model M keyboards, one 1390120, one 1390131 and one 1391401.  These are the Model Ms intended for the IBM PC/XT, IBM PC AT and IBM PS/2 series, respectively.  The first two have the silver IBM badge in the upper right hand corner, the last has a oval gray IBM badge in the upper left corner.

The Model M uses two sheets of plastic for a keyboard matrix and they are sandwiched in between a plastic front and a steel rear.  This base is held together by plastic rivets that were melted and flattened during assembly.  They have a tendency to break off after rough usage, but there are so many that it will take many hard drops before enough break off so that the structural integrity of the keyboard is compromised.  Some people have removed them and drilled screw holes in their place.  The PCB containing the keyboard controller is connected to the plastic sheets and LEDs by plastic ribbons that are easily detachable.  The keyboard also has a metal cable that screws into the back plate (presumably to prevent ground loops) and can also be detached with a flathead screwdriver.

These Model Ms use four non-slotted hex screws.  These can be removed via a long-barrel 7/32" bit.  The keyboard cable on all three is detachable and uses a type of connector called an SDL connector.  It looks like an RJ-45 plug but is wider and has plastic clips on the side that lock it in place.  Even without the plastic clips, the friction between the plug and connector is sufficient for ordinary connections.

My 1390120 was made in 1989, after the IBM PC line was discontinued.  My 1390131 is from 1986 and my 1391401 is from 1989, but made earlier than the 1390120.   It has no status LEDs, which is only occasionally irksome.  Unlike my other two Model Ms, its uses a light gray plastic for the top half of the keyboard assembly.  My other Model Ms use black, which makes the keyboard seem much dirtier if looking down into it.  It also loses the stabilizer bars for the numberpad Enter and + keys.  This is a welcome thing, since removing the stabilizer bars (for cleaning) can often break the small plastic tabs keeping them connected in the first place.  The keyboard also had a tendency to shift a little in its chassis, but a little electrical tape solved that problem.

The Model M has the innovation of using removable key caps over the key stems.  This allows the user to customize his keyboard to a much more advanced degree than the Model F keyboards.  If you want a DVORAK layout, you can make it with a minimum of fuss, assuming the operating system supports it. Removing a keycap is pretty easy.  Unfortunately, this is the reason why you often see keyboards for sale with missing keycaps.

Model Ms can be found for very reasonable prices, Model Fs command huge sums due to their relative rarity.  The Model M does not have quite the level of force required of the Model Fs, and the sound is made by the keyboards is slightly less objectionable to others.  

All three of my Model Ms are autoswitching XT/AT keyboards.  They can work in XTs or AT class PCs without any switches.  My Model Ms do not work in my IBM PC Model 5150, but it is hit and miss which Model M keyboards can do this.  Because they are PS/2 compatible keyboards, they will work in just about any PC, even ones released today, either natively or though a PS/2 to USB adapter.  They will also work in a Mac with a USB adapter.

The build-quality on true IBM Model Ms is fantastic.  IBM made Model Ms from 1986-1992 before they handed them over to Lexmark, which in turn sold the designs and the equipment to make buckling spring keyboards to Unicomp.  I highly recommend scoring an original IBM Model M.  

IBM PCjr. Keyboard 7257

My PCjr. has the second version of the PCjr. keyboard.  The 7257 uses molded keys instead of the chicklet-style keys of the original keyboard.  However, both use the same printed circuit board and the same 62 keys.    These keyboards are rubber dome keyboards, but use a capacitative based approach.  Underneath each rubber dome is a conductive carbon pad that will complete the circuit on the PCB underneath.  The PCB is really thin and the keyboard controller is attached to it.  

These keyboard connect via a wireless infrared transmitter or an optional keyboard cable,  The keyboard cable uses an RJ-11 jack on one end and a unique PCjr. connector on the other end.  Wireless operation requires 4xAA batteries and can last for a few months.  If you obtain one of these keyboards, you may be disappointed to find ancient, corroded batteries inside the battery compartment.  Possible damage to the keyboard may have been caused, but at the very least the corrosion needs to be cleaned out.  The battery contact leads will require special attention, preferably with alcohol, white vinegar and Deoxyit in that order.  Fortunately, the PCjr. keyboard is only held together with Phillips screws.  

The PCjr. keyboard is very light compared to other IBM keyboards and virtually silent because of the rubber domes.  The newer keyboard, with its keys practically touching each other and the key symbols printed directly on the face of the key is much more acceptable to people who value a traditionalist IBM keyboard.  The older keyboard had much more space over the keys and labeled the keys above the keys instead of on the keys to accommodate keyboard overlays.  

This is the only rubber dome keyboard I own, and not out of choice but it is the only keyboard that I have that will work with the PCjr.  Using a PC keyboard on a PCjr required a special adapter with circuitry to account for the low level differences between the keyboards. 

Because there are only 62 keys, the remaining keys required key combinations to activate.  The Fn key was included for this purpose, and this Fn key has been used in laptops starting with the IBM PC Convertible in 1986.  The function keys do not exist, thus the equivalent number key and the Fn key serves the same purpose.  Of course, when programs use combinations like Ctrl F5, this becomes more cumbersome.  Most of the numberpad keys were lost.  The arrow keys pulled double duty as cursor control keys.  Typing the \ key required the use of the Alt key, which DOS users probably did not appreciate.  

Using this keyboard, with its mushy keys, does not give a very good tactile experience.  Moreover, due to the slow processing of keys by the PCjr., you will often have to "race the keyboard buffer".  Fast typing or holding down keys can give you a warning beep from the system telling you that the buffer is full and your key press will not be processed.  Also, key presses are not processed during disk accesses and the keyboard is should be ignored during serial port transfers.  

Tandy 1000 Keyboard

I have two of these keyboards, one for my Tandy 1000SX and one for my Tandy 1000TX.  The 1000 keyboards are physically identical each other and to the MS-DOS compatible (but not really IBM PC compatible) Tandy 2000 computer.  Tandy saw that the 2000's keyboard was good enough for the PC compatible 1000s.  I do not know if the 1000 keyboard works in the 2000, but I know it only otherwise works in the 1000/A/HD/SX(AX)/TX.  The all-in-one Tandy EX and HX have keyboard that function and feel like the standalone 1000 keyboard and share the layout, except their status LEDs are not in the keys themselves. 

The 1000 keyboard, unlike the Model F PC/XT keyboard, has status LEDs for the Num Lock and Caps Lock keys.  It does not have a Scroll Lock key.  It is held together by Phillips screws and uses square cork feet that can fall off over time.  The keys are susceptible to plastic yellowing from UV rays.  IBM's keyboards never seemed to have this problem.  

The keyboard has 90 keys.  Its F11 and F12 and keys are unique and only generally supported in Tandy Deskmate software.  Its inverted-T cursor control keys are unique only via their low level scancodes, their translated scancodes make them appear like numberpad cursor keys.  Nonetheless, this could cause confusion, which is why some programs require you to put the Num Lock on when using a Tandy keyboard. 

The Function keys are arranged at the top of the keyboard instead of on the sides.  This makes many older PC programs more difficult to use because they were written with the function keys were on the side.  Also, there is no easy way to do *.* because there is no distinct * key, and the \ character requires that Num Lock be off (which it is by default).  Ctrl Alt Del is also awkward due to the position of these keys, but the standalone Tandy systems have a reset button.  

One extremely annoying key is the HOLD key.  The closest key on the Model M keyboard is the Pause/Break key, but on the Tandy keyboard, the HOLD key acts something like a universal pause key. Unfortunately, you may hit this key by accident and it appears like the computer has frozen or crashed.  You have to press it again to unfreeze your program.  The key is right next to the Enter key, making it easy to brush up against.

The Tandy 1000 keyboard was designed by Fujitsu.  The keys use 3rd Generation Fujitsu Leaf Switches and use a linear design.  There is a PCB for the keyboard matrix and a a black metal base for holding the key stems and sockets.  The key caps are high quality double shots, with beige over black.  You can remove them with a chip puller, but I am not sure how to remove the spacebar without damaging the two retention clips on the sides, which acts like a stabilizer bar.  None of the other keys have stabilizer bars.  

While the 1000 keyboard does not use rubber dome technology, the keys feel somewhat mushy to the touch.  There is no question, however, that the keyboard was much improved over the PCjr. keyboard.  However, the shift keys are still too small, the enter and backspace keys are also small and the layout is very cramped feeling.

Tandy Enhanced Keyboard

This Tandy keyboard was used for the Tandy 1000 TL and SL computers and the later computers in the line and its other PC compatible computers after 1987.  The Enhanced Keyboard uses the same layout as the Model M.  Like the Model M, it is an autoswitching XT/AT keyboard.  However, the Tandy Enhanced Keyboard did work in my IBM PC Model 5150, even more versatile.  They come with non-detachable cables with a 5-pin or a 6-pin connector.  Unlike the Model M, the status LEDs are underneath the keycaps of the Num Lock, Caps Lock and Scroll Lock keys.  

The keys on this keyboard feel much stiffer than a Model M keyboard.  The Shift keys and the long Enter and + keys feel like they have large dead areas which feel hard to the touch and will not register a keypress.  To be fair, my Model Ms' right shift key also has this issue to a lesser degree.  

This keyboard is a rebadged Fujitsu keyboard, and has removable keycaps like a Model M.  These keyboards use Type 2 Fujitsu Peerless switches.  The key caps pull off without too much difficulty and use dye sublimation like IBM's keyboards.

Also like a Model M, the key stems sit on top of a rubber dome membrane.  The key action is much simpler, there is a spring underneath the key stem that pushes the key back up once it has pushed the rubber dome down.  Not quite as complex as the switch over membrane technology of the Model M, which use the movement of a spring to shift a piece of plastic that makes the two membranes contact each other.  

Dell AT101W

I found this keyboard at a thrift store for $1.00 sitting on a shelf with half a dozen cheap rubber dome USB keyboards.  I was told there were no returns, but the keyboard looked in good enough shape that I felt the dollar was worth it.  The Dell AT101W is my only 104-key keyboard, and its Windows keys and Menu key are the same size as the Ctrl and Alt keys.  Unlike a 101 keyboard, all the keys on this row until the cursor keys, are convex instead of concave.  A Unicomp 104 keyboard has convex keys on this row, except for the space bar.  The Unicomp's space bar is smaller than the Dell's, consequently the other keys on this row are the same size as a Ctrl or Alt key on a Model M.  

This keyboard uses complicated black ALPS switches.  The keycaps required a tremendous amount of force to remove, and I eventually resorted to using a chip puller, which worked well.  All the large keys have stabilizer bars : both shift and enter keys, the plus key, the backspace key, the numberpad 0 key and the spacebar.  This is a bit of overkill in my opinion due to the longevity concerns, but it eliminates dead spots on the right shift key.

The keyboard is not quite as large or as heavy as a Model M, and the keycaps show signs of UV yellowing.  The PS/2 connector has a purple sheath.  Interestingly, the are three channels underneath the keyboard where you can thread the keyboard cable to the left, right or center of the keyboard.  The keyboard is held together by Phillips screws and plastic tabs that are easy to pry open.  The top of the keyboard assembly is a metal plate that showed corrosion from whatever moisture got into the keyboard, just like a Model F.  

I am using this keyboard to type this article.  Since I acquired it recently, it is the only serious experience I have had with it so far.  There is still a sound when the keys are pressed, but it does not have the same harshness of a buckling spring.  The concave of the Ctrl key has gotten some taking used to.  I do not find that I miss the Windows keys since owning a Unicomp 104 some years ago.  The Menu key has always been almost useless.  Even so, after about two days of typing on the keyboard, I find that it is a very good keyboard for the time.  I make more mistakes than with a Model M, but less than with a nasty cheap rubber dome keyboard.  

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