Removing, Disassembling and Cleaning NEC Blue Oval Switches

User avatar
OldIsNew

03 Nov 2019, 23:09

I recently picked up a NEC APC-H412 board with NEC blue oval switches that was in pretty rough shape. At least a third of the switches didn't work at all and the rest were rather scratchy. I figured this would be a good board to have a go at trying to desolder and clean the switches.

Removal of the switches is not difficult but does take some care. Desoldering is rather easy since the holes in the PCB for the switch pins are rather large and not difficult to clear of solder. I used a soldering iron and simple solder sucker and it went rather quickly.

Once the switches are desoldered, they need to be removed for the mounting plate. They are held into the plate by two plastic tabs on the switch sides. I found them fairly simple to remove from the plate using a small flat head screwdriver.

The top of the switch (where the NEC logo is) has a recessed notch:


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I used a small flat head screwdriver angled down towards the mounting plate, and then while applying moderate pressure, used this to lift the top half of the switch up which pops the retaining clips up out of the mounting plate. This should not take a lot of force, if the switch doesn't readily come loose make sure to check that there is no residual solder holding the pins to the PCB:
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The switch can then be removed by hand:
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jsoltren posted a nice video on YouTube that shows a slightly different way of removing the switches as well:
NEC APC-H410E Blue Oval Key Switch Removal



After removing the switches I decided to see if i could repair the non-functioning ones.

The switches are closed by four plastic rivits:
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I used an Exacto knife to carelfully shave the rivets off the case

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The space under the top plate (with the NEC logo) contains the click leaf, the bottom rivets hold the switch plate in place. If you only want to clean the switch plate, and not completely disassemble the switch, you can just remove those two rivet tops.


To remove the switch plate I GENTLY pressed the switch down with the pins on a block of 2x4 (rather than a hard surface where they could slide):
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This lifts the switch plate free:
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EDIT: Although I did find this a pretty quick and simple way to pop out the switch plate, I think that due to the potential for bending the pins, the safest way is to use a small flat head screwdriver to pop the plate up from the top.



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BE CAREFUL if you do this! It should not take much pressure to pop the retaining plate off the pegs. If it is taking much pressure, stop and make sure the rivet heads are completely removed. It is not difficult to bend the pins and potentially break one off, which would ruin the switch.

The top cover can be removed by hand with the edge of a fingernail (which is what I did), but could also use a flat head jewelers screwdriver.
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Then disassembled switches:
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I washed off the plunger and case body under running water and then soaked the parts in 91% IPA and used a cotton swab to rub down the parts.
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Then reassembled the switch. The click leaf goes in oriented as shown below (it seems obvious but I did put them in up side down once or twice and had to go back and turn it around).
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The spring goes back on the peg and the the plunger on top of the spring.
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Be sure to orient the plunger correctly. The longer tab goes towards the switch plate, the shorter towards the click leaf:
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Then replaced the switch plate and the top plate:
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The tops are a little finicky to press back on, but there is an audible click when the pegs do pop back in the holes. There should be no more noticeable gap on the reassembled switch versus an unopened one:
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All the non-functioning switches I have cleaned are now working and have a nice click. The scratchiness is gone too. One other thing, be careful in general when handling the switches to avoid bending the pins since this could result in breaking one off!

The main issue now, of course, is how well the switches will stay together if simple left like this. The top plates did all firmly snap back into place. I have put moderate traction on the plungers without the switches opening, but of course when I pull keycaps at least one top plate does come off (with plunger still in key cap). I'm going to try Loctite Epoxy Plastic Bonder on a couple of switches just to see how that works, but I plan on leaving the majority as they are so they remain easy to open if I need to. I figure if I decide to pull the keycaps I'm just going to have to put the switches back together again - but at least they work now.
Last edited by OldIsNew on 06 Nov 2019, 05:18, edited 1 time in total.

User avatar
OldIsNew

04 Nov 2019, 04:07

A side note on how the switches work. If you test continuity on the switch plate while out of the switch body, you will find the switch is closed. If you press on the leaf on the front of the switch (A in picture below) it moves the "T" contact on the back (B) off the contacts from the pins (C&D) and the switch opens. The plastic tab on the plunger presses on this leaf when the switch is at rest and keeps the switch open. When the plunger is depressed the "T" bar moves back against the contacts and completes the circuit. This is also why the switch activates before the click - the plunger tab on the switch plate side releases the contact before the tab on the other side reaches the click leaf.

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User avatar
OldIsNew

08 Nov 2019, 03:34

As an update, I have tried gluing switches closed using JB Weld Plastic Bonder and it worked well. I tried both a dab of the plastic epoxy on the pegs before reattaching the top as well as dabbing some over the pegs after closing the tops and both methods have worked well. I have placed and pulled keycaps off the glued switches multiple times (ten times as a test), using the recommended method for pulling NEC blue oval keycaps, without any problem. The switches do appear to be permanently resealed and are working well. Of course now those switches cannot be readily reopened and I think I will leave the rest unglued since I like having access if needed - but the switches can be opened, dissembled, cleaned and then permanently resealed with very good results.

In the pic below the top plate was glued with a dabs of glue from above, the bottom plate with glue on the pegs first. I think gluing from the top is probably best since less likelihood of getting glue on internal parts by accident.
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User avatar
abrahamstechnology

08 Nov 2019, 12:35

I'm wondering if we can't use really tiny jewelry/glasses screws or something to put them together.
Same with Futaba switches.

User avatar
OldIsNew

12 Nov 2019, 01:26

I've finished dissembling, cleaning and reassembling all of the the switches on the board, resoldered them and am now using the board. The switches are all working and feel good!

This board was a mess when I got it with at least a third of the switches not working at all, and most of the rest feeling pretty gritty. There was lots of gunk on the PCB as well and to clean it I needed to remove the faceplate, which is held onto the PCB by one screw and five metal rivets.
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I drilled out the rivets. Here's the front of the PCB without the faceplate:
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Used M2.5-0.45x8mm machine screws and nuts when putting it back together.
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All of the switches on the board are identical, except for the space bar which has a heavier feeling spring and a white top case plate.
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I took a picture of the spacebar switch spring (left) and a regular switch spring (right):
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Yes, I would suggest buying a clean, working board rather than doing this - but I hate to see a potentially nice vintage board go to waste. It was a fun little project, and at least it shows these switches can be taken apart and put back together again in good working order.

Finished board:
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abrahamstechnology wrote:
08 Nov 2019, 12:35
I'm wondering if we can't use really tiny jewelry/glasses screws or something to put them together.
Same with Futaba switches.
I like the idea of the screws, but it seems like it would be pretty difficult to do.

User avatar
XMIT
[ XMIT ]

12 Nov 2019, 05:52

I'm really encouraged to see that there is new progress on repairing these boards. Some prior threads, including my own repair from 2015, are here:

viewtopic.php?t=15804
viewtopic.php?f=2&t=10861
viewtopic.php?f=33&t=12076

I would be really careful before gluing a customer's key switches back together. At best the key switch will never come apart again making this a one time repair. At worst the key switch will come apart at a really inopportune time - like inserting a space, to make the benign "sudo rm -rf /home/deleted_user" into the less benign "sudo rm -r / home/deleted_user". Keyboards need to work first and foremost.

Admittedly I tried glue myself - garden variety Krazy Glue cyanoacrylate - and gave up when it didn't stick. I don't know for sure but I believe the key housings on these are made of POM, aka Acetal, Delrin, etc. It's a famously difficult plastic for adhesives.

Since 2015 I've come to take a more polymer science centric view of plastics and adhesives. Even though it is certainly technical marketing by Loctite, this application guide is helpful for selecting an adhesive:

https://www.ellsworth.com/globalassets/ ... onding.pdf

From page 15:

"Loctite® 401TM Prism® Instant Adhesive, when used in conjunction with Loctite® 770TM Prism® Primer, achieved the highest bond strength on all of the acetal formulations that were evaluated."

So, that may be worth a try.

I agree with abrahamstechnology that drilling and screws may be a good idea. You'd need pretty high quality tools - and good fixturing or a really steady hand - in order to do this. But that would be my preferred approach, using either brass or stainless screws.

User avatar
OldIsNew

12 Nov 2019, 22:53

XMIT wrote:
12 Nov 2019, 05:52
I'm really encouraged to see that there is new progress on repairing these boards. Some prior threads, including my own repair from 2015, are here ...
Interesting info thanks for posting! I also don't really like the idea of gluing the switches. I only glued two as an experiment using JB Weld Plastic Bonder which is a urethane based system ( MSDS for Part A and MSDS for Parts A&B ). Using screws would appear to be the ideal solution but it does seem like it would be rather difficult to accomplish.

The glue does seem to work well, but again the problem is that it appears very unlikely to be able to reopen the switches without significant damage. To some extent, however, it appears resealing the switches may not turn out to be such a major issue.

I was careful to just shave the heads off the plastic rivets holding the switches together. When reassembling them they did snap closed with an audible "click" and felt rather tightly closed. Now that they are soldered back on the PCB, I have found that I can pull the keycaps without the switches coming apart - likely largely due to the switch plate side being soldered to the PCB. Of course I am gentle with them using the "rolling" method you described. I'm sure the plate over the click leaf would pull loose if too much force was used. Since the board is just for my own use it's perfectly adequate - but of course it's a different story if planning on doing repairs for someone else.
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Pulled keycaps on 11 unglued switches (F1-11) and one glued switch (F12)
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Pulled Keycaps on unglued and glued switches
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