#0013: Repair of a game controller with fatigued dome switches
What is a dome switch?
In order to know what dome switch fatigue is, we must first identify dome switches. Dome switches are buttons that utilise a dome made from silicon, rubber, polyurethane; or a similar material with the same elastic properties. This dome effectively acts like a spring and pushes the button back up when applied downward pressure is removed.
A typical dome switch will consist of several parts. These are: a (usually) plastic keypad key, an elastic dome, and a graphite pad. The switch key (or button) is mounted onto the elastic dome, additionally the graphite pad is attached to the concave or underside of this dome; and finally, this assembly is sat atop a patch of unconnected unmasked circuit board traces. These traces essentially function as switch terminals.
The idea is that when the downward force is applied to the key, the elastic dome is compressed; causing the graphite pad to press down on the unmasked PCB traces underneath it. This graphite pad actively bridges an electrical connection across these traces, due to graphite’s electrical conductivity.
When the connection is made across these traces, a logic level electric current (around 3.3 volts) is either pulled down to or pulled up from signal ground. It really depends on the IC (Integrated Circuit) chip that is managing and interpreting the keypad array as to the specifics. Anyway, the point is, essentially that is how the computer knows which buttons are pressed and for how long. After the pressing force is removed, the elasticity of the currently compressed dome material causes it to reset to it’s original domed profile. And in doing so it lifts the graphite pad from the traces and breaks the electrical connection.
Example of dome switches within a handset phone
Diagram of dome switch in action
What is dome switch fatigue?
Dome switch fatigue, or more specifically dome fatigue: is when the domes within dome switches, develop a fault due to extended use that makes them no longer effectively reset their position. I.e. pop back up after they have been compressed.
The main symptom of dome fatigue is button sticking. In other words, when a button is pressed down, it either takes longer than it should to reset, or it stays down all together. This is assuming that the keypad is actually clean, as there are many reasons as to why a button might stick other than dome fatigue. Accumulated grease or oils, foreign objects (like food), and dust build up can easily cause button sticking.
Once the device has been opened, the domes themselves can be examined. Look for stress lines: thinner (often lighter) areas of material that can indicate structural weakness. I recommend comparing the suspect dome to it’s known good neighbours; adjacent domes from the same device that occupy buttons that don’t stick. Since they are from the same material stock and often from the same actual moulding as well (as is the case here), it can make spotting any actual stress signs easier. Common sense right?
As you can see in the example picture, there is a stress ring on the one of the four action button’s domes. This dome corresponds to the “A” button on an imitation USB Xbox 360 controller. Now I don’t mean to go on a tangent but I will say that imitation products like this controller are generally made to a price-point. I.e. the manufacturer cuts certain corners to bring the unit price down.
This is done in a bid to undercut the original product and sell itself as a budget alternative. In many cases the cut corners and lower quality product is mostly acceptable to the end user, as it is reflected in it’s price. However, these cuts tend to including: the sourcing of lower quality, less durable materials.
I believe this to be the issue here, although I haven’t had this controller for long. (Approximately a year.) I use this controller to mostly play platformers such as Splelunky. Since the “A” button is used to jump, it is by far the most used button; and it seems like over the time that I have owned it, I have just fatigued this particular dome. Either by some kind of repetitive flex damage (i.e. general use fatigue), or by just pressing too hard on it in moments of panic or frustration during play.
Example of “sticky button”
Example of fatigued dome
Repairing controllers with fatigued buttons
Sadly, an actual and effective repair of the dome itself is outside my capabilities. I just replaced the knackered dome with a fresh one. Well… a less knackered dome from a spares unit. As you can see I chose a third party “4 gamers” brand PlayStation2 controller as a donor unit. This is because that is all that I had on hand at the time. Additionally I am generally unwilling to purchase materials for a repair unless I have to. And to be honest, when it comes to repairing budget electronics such as this controller, it really is hard to justify spending any amount of money for materials, when one could spend a little more and purchase a new unit.
With this repair, I initially intended to replace the entire action button array (all four buttons), with domes from the spares unit. This is because the different types of domes will have different force pressure resistances, and bounce back elasticity. Which would lead to users experiencing different levels of tactile feedback or “button feel”.
At this level, I don’t mind much what the exact tactile feedback of the spares domes are; as I doubt specifying tactile feedback was much of a concern for this budget controller to begin with. Ergo this slapdash replacement wouldn’t necessarily denote a loss in overall device quality or user experience.
However I would mind if the feedback of the grouping of action buttons wasn’t uniform (or near enough). I.e. if one button was noticeably stiffer or mushier. That disparity in tactile feedback may actually become a distraction during play. It may even negatively affect a player’s performance; due to the player becoming accustomed to the tactile feedback of one button and then because of that either pressing to hard or not hard enough when they move onto another button (with a different level of resistance) in order to perform a different action. It may cause a misclick; either registering two inputs, if the new dome is significantly weaker/squishier or none at all if the new dome is significantly stiffer than the previous.
Unfortunately, I ended up just replacing the tired dome and using the rest of the three originals. Even though I have a picture of all four action button domes replaced on the controller. I dropped one on the floor shortly after that; and after 30 mins of searching. I just adapted to this strategy. In this case the new dome and the originals have similar (although not the same) level of tactile feedback to them. They aren’t different enough to be an issue. Not for me at least.
Spares unit
Application of spare dome(s)
Demonstration of device repair (before and after)
Original fatigued dome switch (green “A” button)
Although tactile feel can not be conveyed: notice the mushier, softer sound from the green “A” button when compared to the others.
Replaced dome switch (green “A” button)
The sound produced from the replaced dome is similar to the other three buttons, although they are not uniform themselves. There is an acceptable level of difference within tactile feedback across the buttons. The sound of the buttons when pressed reflects this.
Final thoughts
To sum up my basic ethos when it comes to repairing a device with fatigued domes. One, one has to replace the domes. As far as I can tell the domes themselves are irreparable. Two, When replacing the domes, it may be better to replace known good domes in a bid to get a uniformity of tactile feedback on all the buttons on a device, or at the very lest on a significant button grouping. Such as action buttons or directional (D-Pad) buttons. That’s the takeaway.
That’s all folks. Thanks for reading.
References, links, further reading
“Diagram of dome switch in action” gif taken from: https://i.imgur.com/5K9Uy.gif
https://www.mechanical-keyboard.org/advantages-and-disadvantages-of-mechanical-keyboards/
https://en.wikipedia.org/wiki/Keyboard_technology#Dome-switch_keyboard