Removing, Disassembling and Cleaning NEC Blue Oval Switches

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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:

T_notch_SM.jpg (198.53 KiB) Viewed 284 times

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:
U_screwdriver_SM.jpg (281.32 KiB) Viewed 284 times
V_lifted_SM.jpg (188.77 KiB) Viewed 284 times

The switch can then be removed by hand:
W_removing_SM.jpg (264.48 KiB) Viewed 284 times

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:
A_orig_SM.jpg (135.18 KiB) Viewed 284 times

I used an Exacto knife to carelfully shave the rivets off the case

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C_one_rivet_SM.jpg (125.87 KiB) Viewed 284 times
D_all_rivets_SM.jpg (143.79 KiB) Viewed 284 times

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):
E_remove_plate1_SM.jpg (230.05 KiB) Viewed 284 times

This lifts the switch plate free:
F_remove_plate2_SM.jpg (114.55 KiB) Viewed 284 times

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.

G_diss_1_SM.jpg (102.87 KiB) Viewed 284 times

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.
H_diss_2_SM.jpg (111.66 KiB) Viewed 284 times

Then disassembled switches:
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J_diss_4_SM.jpg (179.97 KiB) Viewed 284 times
K_diss_5_SM.jpg (164.46 KiB) Viewed 284 times

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.
L_soak_SM.jpg (302.58 KiB) Viewed 284 times

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).
M_replace_1_SM.jpg (204.8 KiB) Viewed 284 times

The spring goes back on the peg and the the plunger on top of the spring.
N_replace_2_SM.jpg (123.84 KiB) Viewed 284 times
P_replace_3_SM.jpg (100.35 KiB) Viewed 284 times

Be sure to orient the plunger correctly. The longer tab goes towards the switch plate, the shorter towards the click leaf:
O_orient_tab_SM.jpg (152.41 KiB) Viewed 284 times

Then replaced the switch plate and the top plate:
Q_replace_4_SM.jpg (120.83 KiB) Viewed 284 times
R_replace_5_SM.jpg (175.6 KiB) Viewed 284 times

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:
S_reassem_SM.jpg (118.91 KiB) Viewed 284 times

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

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.

switchplate_both_marked.jpg (162.65 KiB) Viewed 245 times

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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.
glued1.jpg (125.61 KiB) Viewed 160 times

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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.

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