best method to restore conductive keypads?

[coppercone2]

My wavetek 399 has a rubber keypad with the carbon stuff on it.

I need to press very hard with a implement to get it to register. I cleaned them before and it did not really help.

I see there are a whole bunch of methods to repair them, from gluing on conductive plates, to putting conductive glue on, etc. What works the best and is most durable?

[Psi]

Check with a DMM using a very light touch to see which side is the problem (higher resistance).
Either the carbon pads inside the rubber buttons or the pcb carbon tracks.
(It's probably the carbon pads on the rubber buttons)

If that's correct, then you can probably order some carbon sheet or carbon pads and cut them out to stick pieces inside the buttons to restore them.

[coppercone2]

what should a good resistance be to light probing? ANd they are over gold tracks, those are fine.

I am gonna stick it in a hot ultrasonic for a while incase it got contaminated, maybe that will help.

How about silver paint? Silver epoxy?

[Psi]

The rubber buttons are usually covered in carbon and this can wear away/crack because the buttons move.

You could try some silver paint/silver epoxy however i feel that it will crack under the flex of pressing the buttons.

I would try to find a sheet of carbon intended for button use.

Or you could probably find some junk electronic device with carbon buttons and pry out the pads using a knife and then glue them into your defective keypad buttons.

[coppercone2]

do they have high flex paint or coating that is conductive? Like silicone? Mix silver powder in 2 component silicone?

The idea of... cutting all that crap is really awful

[coppercone2]

And while the coating can crack, so can the adhesive. I have a feeling adhesion to those rubber membrane is gonna be dodgy at best.

[Psi]

if you search aliexpress for "Rubber Conductive Buttons" there's lots of things you could order for couple of dollars to pry out the conductive pads from.

[coppercone2]

I am going to try this, I did not realize major electronics retailers sell it

https://www.chemtronics.com/circuitworks-rubber-keypad-repair-kit

I see a few brands of this kinda stuff.. I am sure someone here has experiance with these products?


I am basically irate at this wavetek 399, I literarly started a few small repair jobs 2 weeks ago because I thought I could clear out some of the simple repairs but it has been nothing but completely annoying and I keep running into bizzare problems like this one not involving electronics. Plastic panels, keypads, clasps, rubber feet, etc

[floobydust]

First I do a wash of the keypad in dish soapy water. Use IPA and Q-tip on the PC board. Modern keypads are just conductive paint for a pad, older gear it's a conductive pad bonded to the silicone.

I now use the conductive rubber repair kits. More here: https://www.eevblog.com/forum/repair/carbon-contact-pad-repair/msg4032652/#msg4032652
My buddy just used that CircuitWorks Rubber Keypad Repair Kit  I'll check how it worked for him.
I did not have success with MG Chemicals (discontinued) keypad repair kit, it used cyanoacrylate which cures hard so flexing made it crumble and fall off.

[coppercone2]

Yeah I tried clean, fader lube, and even deoxit gold on the gold parts. None of them really work too well, if anything the fader lube grease made it work worse, with deoxit gold being neutral or close to it. But I cleaned it up in 20 min of ultrasonic followed by a spray down with IPA and then wipe with IPA q-tips on the carbon.

I ordered the circuitworks one, hopefully this fixes it. I bet there is some surface condition going on from age, that panel was totally disintegrated too, I need to fill that up with flowable epoxy maybe as a reinforcement where I can... but wow I am sick of this thing, total fucking menace, they packed the fail real hard into that interface panel. 

Good lord people go with metal panels and metal mechanical switches, that key pad stuff is not worth it!

500,000 cycles seems quite nice! Might be able to program a handful arb wave with that amount from the front panel before it needs a recoat

[Psi]

Sometimes the carbon coating is very thin on top of black rubber.
It gets worn off completely and no amount of cleaning will get it to work, obviously.

[coppercone2]

ah, I thought it was a poured layer. Like why would you have 2 things to pour instead of one if you are gonna paint it? I guess unless they need different softness materials to get the right feel. Like a brace

[xavier60]

A while back I tried to remove the conductive layer from the underside of the buttons on a keypad using Dremel with a rounded burr.
The burr didn't seem to remove any material, but I found that low resistance was restored.

[coppercone2]

you mean like sand paper or like a carbide burr?

[xavier60]

you mean like sand paper or like a carbide burr?

Tungsten carbide Burr like this one, https://www.hobbytools.com.au/dremel-max-life-9903hp-1-8-3.2mm-tungsten-carbide
My original intention was to remove the black conductive layer to see if an adhesive would work better at sticking on some aluminum foil.

[coppercone2]

ok, those are not the ones you would use for soft material (maybe 2 flute or even 1 flute for mill cutting ) I think. I have that, but I am a little scared that I will rip up the keypad. Maybe I can try it  very carefully. People usually sand very soft materials, they don't have a good reputation for being burred with a burr made for ferrous metal, but in this case it helped. But I am also wondering if you just sand it a little... with a sanding stick. I bought a bunch of sanding sticks.

[xavier60]

I have just tried doing the same to a working TV remote. The burr removed the black conductive material at a slow controlled rate. I think a stone burr would be safer though.
Take care, your results may differ.

[rfengg]

Cleaning either the pcb pads or the carbon on the keypads is a very temporary fix.....in cases where I have to tried to do this on remote controls, the fix lasts for a month or two even if you are very careful with using the remote.......it looks like once the deterioration has started , it's a very hard to prevent its worsening.

My last resort was to get some copper tapes with conductive glue, cut them into tiny circles and place them over the keypad carbon......works better than the temporary cleaning fix.

[TERRA Operative]

I have used this stuff to good effect.
I'm not sure about the long-term durability, but it's not a hard repair to repeat.

https://www.bareconductive.com/collections/all/products/electric-paint

[timeandfrequency]

Hi coppercone2,

You might use some graphite paint
This one dries in minutes.

[Wallace Gasiewicz]

I used aluminum conductive tape. Cut dots  with a paper punch. Worked pretty well.
This worked for a while. I think it wears out the traces on PCB.

[BILLPOD]

I've had good results with this conductive paint.  I apply it with a q-tip.
https://www.amazon.com/gp/product/B01MQ4F1T5/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

[coppercone2]

anyone want to hazard a guess about how much silver powder you need to add to two component silicone to make it conductive enough to work with these pads? I do have 10 grams of silver powder for those sintering experiments that I strayed away from. I would prefer to not waste silver and I have no clue what a mix ratio might be. I noticed conductive silver epoxy does not register conductivity until it cures (with dmm probes), and the cure time of the silicone mix is very long (24 hours IIRC), so its kind of expensive and time consuming to guess.

I bought the repair kit already, but I could try the silicone silver mix if someone has a reasonable answer

[eurgenca]

Isn't copper powder cheaper?
I always use conductive rubber pads with super glue and no problems.

[wraper]

Clean it with dishwashing liquid first, measure resistance of conductive rubber by multimeter. Resistance should be up to a few hundred ohms on good buttons when pushing probes a few millimeters apart. If on bad buttons it's much higher than on working buttons, use fine sandpaper to remove a thin layer of conductive rubber. To do so, push the button so conductive part protrudes outside, then make a few light passes with sandpaper, measure resistance. Repeat until resistance drops <2x of good buttons, then stop sanding. You should remove just a few microns at a time. Be careful to not sand the membrane around the button as it's very thin. Clean PCB with some sort of alcohol too. Use additive repair like gluing conductive part only if conductive rubber is totally destroyed and cannot be rejuvenated by removing outer layer.