IBM Model F PC/XT disassembly

[Chloe]

I got this earlier this week and I love it. It's lighter than the IBM 5576-A01 and sounds similarly musical with a metallic springy sound to every press. Keycaps are one piece and have no home row locators. Volume-wise it beats the KPT-84 as the loudest keyboard I own. At 2.6kg it's also the heaviest, a kilo more than the A01. At some point I'm going to make an adaptor so that I can actually use it.



This one was assembled 10-01-1985 in the UK, part number 1501105. I took it apart for cleaning and noticed the plastic casing is very thick (weighs around 500g alone) and painted (inside is yellowish).



The bottom part of the case is metal with what looks like cork feet. There was alot of dusty fluff inside. Seeing this made me want to clean it thoroughly, although I really didn't want to take the keyboard assembly apart. It's made up of two metal plates with the buckling spring modules and a layer of foam sandwiched in between.

   

I took it apart anyway, and at many points I almost wished I hadn't. It was also a real pain to put back together.


Disassembly

First I twisted the tabs a little at the top of the upper plate, which is painted a dark olive. There is one tab at the end that needs to be bent away, and a screw lies under the foam covering controller part of the PCB.



The two plates hook together at the bottom so the upper plate has to be slid out. This proved to be very difficult as they are a tight fit and have sharp corners, so be careful.



The upper plate has lots of little rust spots that may need to be treated.



The PCB is flexible and can be removed from the lower plate, which is curved. A 14 pin connector is used for just four wires.

   

Each key has its own module which are stuck to the foam. The foam has degraded, leaving little bits everywhere when handled. Unlike the modules in the A01 the rocker actuators do not stay clipped inside. Bear this in mind when pulling the plates apart as some will fall out and might get damaged if they are trapped in between.



I found the space bar a bit too stiff so I tried taking out the stabilizing bar. Pulling the keycap out so it unhooked from the bar wasn't enough, it still acted like an extra spring underneath. Unfortunately the space bar wobbles too much without it so I put it back.

Removing and replacing springs from the rockers is easy (just twist anti-clockwise) because the point is rounded without flat sides like on Model M and A01 rockers. The spring on A01 is a little shorter.




Reassembly

After pushing the modules into the upper plate I sat the upper plate on a pair of these plastic containers so I could fit the rockers so they sat flat.



With the stabilizer mounted the space bar rocker doesn't sit flat. Check the space bar clicks after placing the plate to make sure the rocker hasn't moved. You can see how the stabilizer fits into the keycap.



The upper plate needs to be slid back into lower plate hooks without disrupting the rockers. I used these small plastic clamps to hold the plates together whilst I tapped the plate into place with a hammer. As you can see the space bar needs to be fitted first. There is no way to hook the stabilizing bar into the keycap later on.

[lal]

What a *great* HOWTO and very interesting info. I wouldn't have thought that it's painted. Maybe after all there is a way to paint a beige Model M that does not look like s**t. Really good work, switch kitten

[Chloe]

Thanks guys.

[Mercen_505]

I'm still waiting to get my hands on an 84 key AT model F. The sound of the keys chattering as you type on an F is just *unbelievable*.

[Chloe]

The date on inner metal plate is 1984. The inside of the case is also stamped 1984. The dirt inside was mainly on upper metal plate, there was loose fluff as well. I think something had spilled but it hadn't reached the rockers or PCB. The PCB was only a little dusty.

[JBert]

Interesting to finally see one disassembled (and quite courageous of you, seeing how I read other reports in the manner of "don't even think about it").
Is there really no way to take it apart more easily? I was thinking of securing the cap-less spring and rockers with some metal wire so they wouldn't fall out once the plates are separated.


Also, I was wondering: did you find a way to un-stiffen the space bar? I have the habit of pressing the spacebar with the tip of my thumb. When I dusted off the XT and tried to type some stuff with it, it did strike me as annoying. Pretty sad actually, all the other keys seem to work great...
Of course, learning to press it some other way on it is still an option, were it not that habits are hard to change.

[ch_123]

I've been told (by Sandy) that removing the space bar on the Model F is a bad idea, as reinserting it would require disassembling the whole assembly. I assume that is true for the XT Model F as well as the AT one. If you want to do so, Chloe's guide is a good reference, but I'd just try to get used to it. It is definitely one of the weaker points of the Model F design.

[chimera15]

The keys are partially melted too.

[ch_123]

Took mine apart earlier on to give it a much needed clean, found this guide invaluble for fixing it up. Some interesting things I noticed on mine - one is that there are contacts that would in theory allow you to turn it into a more Model M like layout (there are contacts on each end of the space bar which would correspond to the location of the alt keys, one between shift and z for the \| key on an ISO layout, and one for the same key on the ANSI layout is covered by the large enter, as is a contact for the #~ button on the ISO layout) but none of them do anything you complete the circuit. I'd be very interested to know if someone knows a way to "enable" them, but I wouldnt count on it.

I also tried to figure out what exactly it was that gives Model F their distinctive feel over a Model M. I was thinking that it might have been something to do with it striking a capacitive switch instead of a membrane, or something to do with the spring/hammer. I assembled a test switch (unlike the model M, the little shafts which house the springs are removable) and tried it on different surfaces. The surfaces affected the amount of flex I felt, but not the feel of the switches, so I guess it's either because the F has a different type of spring, or the different shape of the hammer somehow impacts the tactility of the keypress. Because there is less resistance required to press the key, I'm thinking it's the spring.

EDIT: If the A01 springs in Chloe's pics are the same length as the Model M's ones, then the fact that they are shorter than the Model F's would probably explain it. Goo on Unicomp, put longer springs in your boards!

[msiegel]

besides a softer spring on the model F, the springs seem to buckle later in the keystroke.  i'm more likely to bottom out on the F, but only lightly because the buckling action is smooth and crisp.

the F also doesn't have a rubber sheet under the hammers, so there's less damping.

it would be fun to move those key-modules into a more modern arrangement, if a matching upper plate and pcb could be fabricated

[microsoft windows]

Interesting to finally see one disassembled (and quite courageous of you, seeing how I read other reports in the manner of "don't even think about it").
Is there really no way to take it apart more easily? I was thinking of securing the cap-less spring and rockers with some metal wire so they wouldn't fall out once the plates are separated.


Also, I was wondering: did you find a way to un-stiffen the space bar? I have the habit of pressing the spacebar with the tip of my thumb. When I dusted off the XT and tried to type some stuff with it, it did strike me as annoying. Pretty sad actually, all the other keys seem to work great...
Of course, learning to press it some other way on it is still an option, were it not that habits are hard to change.

On a Model F, the stiff space-bar occurrs in most, if not all of them, XT and AT. Many people believe this is because of the space-bar's construction since it is longer than the space-bar on most keyboards today. However, like others have said, taking it apart to clean isn't a good idea as you will have to disassemble the entire assembly to put the space-bar back in.

The best thing to do with the stiff space bar is to just get used to it. Messing around with it is more trouble than it is worth.

[JBert]

On a Model F, the stiff space-bar occurrs in most, if not all of them, XT and AT. Many people believe this is because of the space-bar's construction since it is longer than the space-bar on most keyboards today. However, like others have said, taking it apart to clean isn't a good idea as you will have to disassemble the entire assembly to put the space-bar back in.

The best thing to do with the stiff space bar is to just get used to it. Messing around with it is more trouble than it is worth.

I did take it apart in the meantime. As it turns out (and has been said before), the space bar has no regular stabilizer bar. Instead, it has a metal spring bent like a V in both the horizontal and vertical plane to give enough clearance for the buckling spring while at the same time pushing the key-cap back up.

I first set out to look for some other stabilizer but without success. In the end, I carefully bent the spring until it was almost flat when looked at it from the side. I wouldn't really recommend it for everyone, but it seems to have gotten the job done for me.

YMMV, so keep it in its original state if you can live with it.


Also, assembling it is mainly a matter of having the right tools: a set of 4 clamps, some nylon fishing wire, some stuff to keep the board stable if it lies upside down, a piece of wood and a hammer.
It took me 2 hours, but only because I hadn't got all of the above.

[ch_123]

What do you need the clamps for?

[JBert]

What do you need the clamps for?

I used them to clamp the backplate on to the front plate so the latches would line up and no key springs can fall out when you hold the whole thing upright.

[ch_123]

I did it in a different way. I remove all the keycaps so that the springs would sit properly in the barrels when turned upside down. I then placed the bottom plate over the top one while still holding it upside down, pressed it together with my hands, and then quickly slid it together by pushing on one end while pressing the other into the floor at an angle. Somewhat crude I guess, but saves the need for clamps.

Oh, of course, you do need to leave the space bar on, but if you're careful about what you're doing, it isnt a problem.

[JBert]

Ah yes, you shouldn't forget to remove those keycaps if you don't want to see rockers jumping around...

I tried to simply slide it together and it wouldn't let me, the latches didn't line up until I held them in place with the clamps.

I actually held the spacebar rocker in place using the fishing wire, hence no trouble from that one.

[ch_123]

Could be an XT-specific issue. The ATs one slide together reasonably easy, although it can take a bit of effort to get the two plates pushed toghether so that the latches line up.

[andrewjoy]

I just got my f today and the space bar is quite stiff i did not read ahead and i will have to fully dissemble to re attach the stabiliser but that can wait for another day the F is clean and is now in uk layout as opposed to the German layout (RIP model m )at the mometnt is is clean and my fingers are getting a workout

the sound of this thing is just amazing if i could sort the space bar out it would be amazing i don't think i like it this stiff

[fohat.digs]

I guess that I am lucky to have large strong hands that enabled me to put the plates back together without clamps on XTs and ATs. I even did it a few times on the big F-122s until I got frustrated and bolt-modded them. Maybe I am just stupid or careless, but I never seem to hit it just right the first time, and end up taking it back apart at least once for some silly reason.

That spacebar issue on the XTs and ATs is frustrating. That separate under-carriage stabilizer seems to do a good job of stabilizing, but makes for a massive assembly to have to move around. I got pretty good at disassembling and re-assembling them, but it takes juggling threads and weights and other silly maneuvers, and still does not fix the basic mass/size/balance problem.

Fortunately/unfortunately, the F-122 spacebar is almost like the Model M, meaning a nice size and weight, but unfortunately it uses a different gauge wire (smaller) so that it won't interchange.

[andrewjoy]

i think the solution is to get hold of 2 switch assemblies and mod in 2 keys next to the space bar and sue the m space bar with a home made holder of the stabiliser on the plate