IBM 5251 Beam Spring Restoration

User avatar
darkcruix

18 Apr 2019, 08:27

IBM 5251 Beam Spring restoration

I already posted a restoration document around a full-size 3278 a while back: IBM 3278 Beam Spring Restoration. The majority of the tasks are the same, with a few exceptions. I also want to say some words about my previous post, as I have learned several things since then. One example is that spray painting a keyboard is not the best of ideas, as during usage, our hands constantly scratch the surface and the oils they produce don’t work well with it, either. Powder coating is the right way to refurbish the outside.

The Initial look at the Situation
My IBM 5251 in the original unrestored state was way more rusted than the previous boards I had in my hands. I have seen worse ones on photos, but not in person. Nevertheless, I had a lot of fun in doing the restoration:
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I feared the worst before opening the Metal Assembly Board. Not knowing what was ahead of me, I had no doubt that I have to do a proper job in de-rusting.
The Keyboard Parts
In my last post, I forgot to explain the different bits and pieces of a complete Beamspring keyboard, hence I’ll do this now:
Spoiler:
  • Key or Switch Module
    • (1) Switch Housing
    • (2) Slider with riveted beam spring
    • (3) Fly plate
    • (4) Return Coil
    • (5) Rubber Damper or Washer
    • (6) Plunger or Metal Stem
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  • Pad Card (Two-layer PCB covered in insulating substrate)
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  • Metal Assembly Board
    • (1) Metal Switch Housing
    • (2) Foam
    • (3) Gaskets (shown on the second picture)
    • (4) Dust Cover to left and right
    • (5) Bottom Switch Plate (that holds everything together)
    • (6) Bottom Case
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Recommended list of items you need / need to prepare for a full restoration
Spoiler:
  • 15mm Steel Hole Punch
  • Paper Towles
  • 2mm Craft Foam (I used EPDM foam band with 100mm width and 2mm thickness and adhesive side)
  • Tape Measure
  • Scissors
  • White Marking Pen
  • Heat Gun or Hair Dryer
  • Containers for the Switches and PCB
  • Rubber Gloves
  • Work Bench or Table
  • Mild Soap and Wash Bucket
  • De-rusting tub that fits the largest parts
  • Evaporust (I needed 2 liters – ca. ½ gallon)
  • Ballistol Spray
  • Micro Fiber Wash
  • Paper Grocery Bags for Trash
  • 3M respirator
  • Goo Gone
  • Guillotine Cutter
  • 3M Acid Free Double-Sided Tape
  • Isopropyl Alcohol (really important)
  • TIME (take your time with this so you don't have to start over)
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Part 1: Disassembly of the keyboard
Taking a 5251 apart is very straight forward. Remove the bottom screws on the case, turn it around and lift of the outer case. Next, remove all keycaps using a wire-keycap remover. They sometimes are hard to remove but pull with some force upwards and wiggle it up- and downwards. They eventually come off.
Once you removed the contamination shield (peel off) and the controller (2 more screws), you should end up with a view like shown below:
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The contamination shield beneath them is always at a state that you can’t re-use it. In all fairness, it isn’t really required anyway. Remove it carefully. You can also get rid of the initial dirt and plastic shield from the keys. I used a vacuum cleaner at this stage.

Unscrew the switch housing from the bottom case, turn it around, so the top side of the switches look away from you, like shown below:
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You now can unscrew the Bottom Switch Plate, which now looks towards you. It contains eight screws in total. Once done, lift it off. You should be able to remove three pieces now, the Bottom Switch Plate, the Pad Card (PCB) and the insulating rubber mat. Put them aside – you should be able to see the switches now:
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Remove all individual key switches by carefully wiggling them out. They should get out fairly easy. Place the switches on a cardboard or in a box (not a big thing if they fall apart, we will dis-assemble them anyway later on).

Most likely you will have a disintegrated foam in front of you after the switches are removed and you will look at something like in the picture below:
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Part 2: Switch Plate Restoration
Step 1: Remove the plastic gasket strips
I could easily remove the gasket strips by slowly pulling on them. Make sure you don’t rip them apart, but if they contain a ton of goo – don’t worry. Put them aside for now.

Step 2: Remove the two Dust Covers
On each side of the switch-plate are two plastic covers. They are only clipped in and can be pulled away easily.

Step 3: Clean the switch plate (get rid of the foam or what is left over)
Originally, the foam was on top of an adhesive plastic strip. There are two ways to remove the foam and strip. Either way, get gloves on first (believe me).
Either you use a heat gun and remove the plastic strip together with the rest of the foam (which would be the preferred method) or you do it like I had to do it (the foam was too much dissolved already).

I first removed the foam using a small palette-knife. After I removed the black foam, I went with a heat gun. With the same palette-knife, I could remove most parts of the plastic strip underneath. Even when I was finished, the switch-plate was still full of goo and rust. This combination is hard to come by. I used a brush to get most of it off.

As rust was the dominant thing left, I took a tub, placed the Switch Plate in it and emptied two bottles of Evapo-Rust on top of it. To cover the full switch plate, I also added another two liters of water (this will increase the time required to de-rust and I had to leave it in the solution for 7 full days).
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Meanwhile:
Step 4: The plastic gaskets
To get rid of all the glue and dirt from the two strips, place them in a bath of Isopropyl Alcohol. Make sure they are completely soaked for at least 20 minutes. After that, take a cloth and spend a lot of time and effort to make them as clean as possible.

Congratulations at this point you have already reached a point where it starts to get a bit easier and less messy. As you might also have to wait for the de-rusting process, in case your switch plate looks as the one I had, you can now concentrate on the Beam Spring Switches.

Part 3: Beam Spring Switch Restauration

The switches are not only expensive, but also rare these days, please work on them only, if you have enough time at hand.

Preparation:
Get at least six large enough boxes ready for the parts of the switches. As described already in the beginning, there are 6 primary parts and I showed also a picture of them earlier.

Step 1: Taking the Switches apart:
There are multiple ways described on how to take the switches apart. For me, the easiest method was a plastic box which could be split apart. I drilled a hole into one end that had the diameter of 10mm. This box is only to get a better grip and limit the possibility of damaging the switch (yes, again, they are expensive and rare).
Now, place the switch in the one half of the box, so that the metal stem and O-Ring are on the outside and the rest of the switch on the inside. Then take pliers, grab the metal stem and pull on it (sometimes as hard as you can). The stem will slide out and the whole switch can be disassembled. As I had to do this about 90 times, I spent half a night on this task and had sore muscles in arm and shoulder the next day.
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Step 2: Cleaning the Switches:
Plastic Switch Housing:
I put the Switch Housing, Slider, Return Coil, Rubber Damper and Plunger (but not the Fly Plate!) into a bath with mild soap for a day. After that, I cleaned them with a tooth-brush and clear water. At the end, I put them in an Ultrasonic cleaning bath and finally rinsed them in de-mineralized water.
Dry them by placing them on a towel for 24 hours.
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Step 2: Coil and Plunger de-rusting and cleaning
Some of the coils have not only been dirty, they also have accumulated rust. Even, if you don’t see rust on your coils at first sight, the de-rusting is super important. The stems on this 5251 have accumulated a lot of rust and needed treatment as well.
Put about 25mm or 1 inch of Evapo-Rust fluid in a plastic box. Add the Coils, Plunger and Space bar and other Stabilizer Wires to the bath and leave them in there for at least 1 day. I left them in for 2 days due to the condition.
After the evapo-rust procedure, I cleaned them with de-mineralized water and let them dry in the sun.
After they have been dry, I put a layer of Ballistol on the parts and let them sit for a day before I used a paper towel to get rid of excessive oil.

O-rings:
The O-rings have been dirty as well, I cleaned them with Soap-water and put them into the Ultrasonic Bath. Finally they also got a little Ballistol to bring back the shine.

Fly-Plates:
I only used some alcohol to get rid of some of the dirt but did not bath them or anything else.

Step 3: Assembly of the switches
After the procedure above I assembled the switches again. This is super easy to do. First take the white slider and clip in the fly plate at the bottom. Then give it a push and the fly-plate should snap up. Put it aside and grab the black switch housing, put the coil on top where it fits in and then drop the O-ring into the middle of the coil.
Next, insert the white slider from the bottom into the housing (there is only one way that works smoothly), so it looks out of the top. The O-ring and coil should be at the outside. Finally take the Plunger and push it into the white slider. The orientation is not important. With a plastic plate I pressed on top of it. There are actually two distinct clicking sounds that tell you that it is firmly inserted. You will see that this needs much less power to do.
Put the assembled switches into a box and make sure they don’t get exposed to dirt or dust.

Part 4: Switch Plate Assembly
Step 1: Replacing the foam
Replacing the foam is one of the most important tasks that you need to do. Especially, if the keys are wobbling around. I also found out that the sound is very much dependent on a proper fitting of the switches.

First of all, you need a foam that is cut to a size of 435mm by 100mm (2mm thickness). In my case this was simple, as I already had a 100mm wide band that I only had to cut at 435mm. I used a Guillotine cutter for this to get a very straight cut.

Next, I placed the foam underneath the switch plate so that the side of the foam was looking towards me. You need to align the foam perfectly at this point and I used glue strips to hold it in place.
Next, I turned the switch plate around and started to mark every hole with a white marker on the foam.
Once every hole is marked, the switch plate (template) can be put away and we can concentrate on the foam.
Use the 15mm Steel Hole Punch, place it on top of each marked circle and punch out the hole. In my case, I only had to put some slight pressure on it and wiggle it a bit to punch the holes into the foam

Once all holes are punched, I put the foam away, as the Switch Plate wasn’t ready, yet.

Step 2: Finishing the de-rusted Switch Plate and Spray Painting of it
The Switch Plate was de-rusted in my case, but the bare metal was facing towards me. I took sanding paper (400 grid) and sanded down all little spots of rust that I could still see. Finally, I gave the whole plate some more sanding.
In a last step I used de-mineralized water to clean it completely and gave it a final inspection.

I put the switch plate on hooks and gave it a nice spray coating using a black paint that is helping to keep rust away. I let it dry for 24 hours.

Step 3: Back to the Foam
Once the Switch Plate paint was completely dry, I took the foam and removed the adhesive protection. Carefully I aligned the foam and glued it to the switch plate like shown below.
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Step 4: Attach back the plastic gaskets
I used double-sided adhesive strips to glue them back on. I placed the double-sided strips on the plastic gaskets themselves and first and finally glued them on the edges (at this time I also added back the plastic side panels).

Step 5: Attach Switches into Switch Plate
Place the switch plate upside down into the bottom case and use two screws to hold it in place. Previously I used books, but this method works perfectly fine (thanks AJM). In the picture you see me using the previously mentioned method using books (works also).
Stick the Switches through the holes in the switch plate. Make sure the orientation is correct and the blind switch for the Space Bar is on the correct spot:
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Finally, align the PCB, Rubber Mat, and Bottom Switch Plate with the screw holes in the Switch plate. Screw them back onto the underside of the keyboard in its housing in the correct orientation. You will see that the switches are pressed much harder against the switch plate and won’t wobble as much.

Part 5: The Final Steps
Before screwing everything back together, I also cleaned the top case for a full day in cleaning agent and rinsed it afterwards in clean water.
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I also added an xwhatsit controller and made some modifications to the keycaps. I don’t want to get into details during this restoration guide, but the final outcome looks like this:
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User avatar
lucar

18 Apr 2019, 17:25

Hi! Great work! And lucky owner !!

Do anyone know if the crossed grooves in the lower metal plate have any use?
I always ask myself why did IBM bother to make that grooves...

Image

Are they functional to the PCB , capacitance or whatever?

Luca

User avatar
darkcruix

18 Apr 2019, 18:31

They are just for higher stability - the stuff is built like a tank ;)

User avatar
inmbolmie

19 Apr 2019, 19:21

lucar wrote:
18 Apr 2019, 17:25
Hi! Great work! And lucky owner !!

Do anyone know if the crossed grooves in the lower metal plate have any use?
I always ask myself why did IBM bother to make that grooves...

Are they functional to the PCB , capacitance or whatever?

Luca
There is a plastic sheet between the plate and PCB with the same groove pattern so that it fits the plate perfectly, that sheet is there for insulation, protection and to press the PCB uniformly against the switches. I suppose the groove pattern is there for better fitting of that plastic sheet.

Can be seen in this post, step 7

viewtopic.php?t=19574

User avatar
darkcruix

19 Apr 2019, 20:29

Hi,

great info. My insulation mat did look completely different (as did the PCB):
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User avatar
lucar

26 Apr 2019, 00:18

inmbolmie wrote:
19 Apr 2019, 19:21
lucar wrote:
18 Apr 2019, 17:25
Hi! Great work! And lucky owner !!

Do anyone know if the crossed grooves in the lower metal plate have any use?
I always ask myself why did IBM bother to make that grooves...

Are they functional to the PCB , capacitance or whatever?

Luca
There is a plastic sheet between the plate and PCB with the same groove pattern so that it fits the plate perfectly, that sheet is there for insulation, protection and to press the PCB uniformly against the switches. I suppose the groove pattern is there for better fitting of that plastic sheet.

Can be seen in this post, step 7

viewtopic.php?t=19574

Thanks all for the info !!
Luca

User avatar
lucar

26 Apr 2019, 00:27

darkcruix wrote:
19 Apr 2019, 20:29
Hi,

great info. My insulation mat did look completely different (as did the PCB):

IMG_2538.jpg
Is that mat a new one or just the one that came with your beamspring?

User avatar
darkcruix

26 Apr 2019, 01:28

It came with it and looked like it was in there from the beginning (had a ton of rust on it before cleaning).

User avatar
AJM

26 Apr 2019, 12:43

inmbolmie wrote:
19 Apr 2019, 19:21
There is a plastic sheet between the plate and PCB with the same groove pattern so that it fits the plate perfectly, that sheet is there for insulation, protection and to press the PCB uniformly against the switches. I suppose the groove pattern is there for better fitting of that plastic sheet.

Can be seen in this post, step 7
viewtopic.php?t=19574
In my 5251 the plastic/rubber sheet looked exactly as in this picture.
But that sheet is completely flat. The pattern was only transferred by oxidation (or something like that) from the plate to the rubber sheet.

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