Repairing/replacing rubber dome switches - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: June 11, 2017, 04:47:43 am
content: I have a couple of old Sega Master System II controllers which are starting to develop problems. I've given the contacts and carbon pads a good clean with 100% IPA, they've improved, but still aren't perfect (probably from many years of being mashed and abused).My question is, is there any easy replacement for these types of switches? Is there a better option than the carbon pads? The rubber domes themselves are fine, but I suspect the carbon contacts are just worn.On the PCB itself there are just exposed traces (see attachment).

author: LabSpokane
author_rank: Super Contributor
timestamp: June 11, 2017, 05:05:35 am
content: Quote from: Halcyon on June 11, 2017, 04:47:43 amYou could try exposing a fresh layer of carbon by very very lightly sanding the pucks with 600 grit sandpaper, but those PCBs really look like the problem. The manufacturer skipped silkscreening a layer of carbon onto the contacts, and now the contacts are worn and oxidized. I'm not sure at this point that you can do much that is more than temporary. The good part is, that since they are passive PCBs, designing new replacements would be fairly easy.

author: Halcyon
author_rank: Unknown
timestamp: June 11, 2017, 05:10:59 am
content: Quote from: LabSpokane on June 11, 2017, 05:05:35 amThe attachment is just an image I found on the net, the pads on my controllers are actually in very good condition with no oxidisation (I cleaned them up with a little DeoxIT contact cleaner anyway), which is why I suspect the carbon pucks. Even with IPA, black stuff was coming off them, I didn't want to go too hard on them as I'm guessing a lot of the crap was actually the carbon layer coming off?

author: LabSpokane
author_rank: Super Contributor
timestamp: June 11, 2017, 05:29:05 am
content: Quote from: Halcyon on June 11, 2017, 05:10:59 amOK, that's different. They're decaying. FWIW, the pucks I've seen used were actually maybe a mm or so thick. You might be able to sand off the rotten material and get down to good material. Or not. In any case, it will be temporary. You could try cutting off carbon pucks from a sacrificial device like an old remote and gluing them onto the old pucks.There are "fixer" kits for sale on Amazon:https://www.amazon.com/ButtonWorx-remote-button-repair-kit/dp/B017OIKGMW/ref=pd_bxgy_60_img_3?_encoding=UTF8&pd_rd_i=B017OIKGMW&pd_rd_r=FZVSHP0Z2DBF48EWPKHH&pd_rd_w=YpeXL&pd_rd_wg=hVLTW&psc=1&refRID=FZVSHP0Z2DBF48EWPKHHI've never used these before, but they might be a good gamble if your pucks are truly disintegrating.You could also try soldering a low profile microswitch onto the existing contacts and have a "clicky" switch. That process could be really fussy, but I'd try it if nothing else worked.Lastly, I'd just design new PCBs with SMT switches that fit under the domes if this was something I used a lot and wanted a long-term fix.This is the type of switch I'm thinking about. You might be able to solder its contacts between the contact fingers on your PCB. I'm not sure how many cycles these switches are rated for, but at less than $0.10 ea on eBay, it definitely wins the cheap prize.

author: floobydust
author_rank: Super Contributor
timestamp: June 11, 2017, 05:57:58 am
content: For repairing remote control and gaming keypads, I tried theMG Chemicals 8339 Rubber Keypad repair kit."Guaranteed to work over 50,0000 keystrokes..."You basically apply conductive silver paint to the rubber, with krazy glue adhesive. It did not last for me because the result is a hard crunchy silver paint that rubbed off in short time. YMMVNext, I am now usingVelostat/Linqstat conductive film(eBay) and gluing a disk on the old rubber. Thicker 8mil is a bit bettter to work with. {It used to be used for ESD bags years ago. Today apparently works for makingtinfoil hats, lol}Problem is Velostat is polyethylene and so no glue adheres to it. Tried everything. Only thing that worked istwo-part cyanoacrylatefor difficult plastics.

author: jonovid
author_rank: Super Contributor
timestamp: June 11, 2017, 06:04:33 am
content: My answer is get one of this box's of Tactile Push Button Switch's sold as Car Remote Key Button Microswitchssold on aliexpress.com item name is10 Types Tactile Push Button Switch Car-Keys Remote Key Button Microswitch

author: Ian.M
author_rank: Super Contributor
timestamp: June 11, 2017, 06:45:20 am
content: My experience of renovating elastomer keypads is that, provided there are no tears or splits, and there is enough conductive elastomer pad thickness remaining, and the board contacts aren't worn away or badly corroded or oxidised, its just a matter of thorough cleaning of the elastomer to remove buildup of contaminates and exuded plasticiser, usually with detergent and warm water followed by rinsing and finally swabbing with IPA, then exposing fresh contact surface on the pad.However any sort of sandpaper is usually too abrasive and risks leaving a rough surface with embedded grit which may not have high enough conductivity. I found the best option was to take a sheet of copier paper, put it on a hard surface and scrub each contact pad across it in one direction, by pulling the elastomer mat while pressing the button. Done right you leave a distinct black streak, stripping the surface of the pad. Use a fresh area of the paper for each pad.I would then test the keypad mat and the PCB without fully reassembling the device, and check all keys responded to light pressure - if any didn't respond or heavier pressure was required, they were given another scrub on the paper. If you've got a suitable scrap PCB with gold plated interdigiated contact fingers, you may be able to set up to measure the contact resistance in a semi-repeatable manner so you can quickly check each pad before and after scrubbing it to determine if more work needs to be done.I've never had good results with any sort of pad repair - the elastomer involved is usually some sort of silicone and it is extremely difficult to reliably bond to it while retaining flexibility. You may get good initial results, but it almost invariably fails again long before any remaining unmodified buttons fail, usually by the replacement conductive pad or surface flaking off or becoming detached from the dome.

author: Gregg
author_rank: Super Contributor
timestamp: June 12, 2017, 05:31:05 am
content: The short term fix is to rejuvenate the carbon on the pads with a soft graphite pencil; i used to do this a lot on early calculators.