I tried to fix a keyboard that was having some intermittent issues by cleaning the conductors on the ribbon cable. I used an emery-board to rub off the rust and patina on the pins at the end of the ribbon, but it turns out that the pins are really soft metal and I ended up rubbing off the conductors themselves.

The ribbon had a little bit of slack so, I trimmed it to where the first break in the conductors were so that I could insert the remainder into the slot. Unfortunately there was not enough metal left exposed to make the connection (<1mm on some of the pins).

I thought about different ways I might be able to expose more of the metal but considering how fragile it already was, I figured that scraping or rubbing the plastic covering was out of the question. I considered using a chemical to dissolve some of the plastic, but I have no idea (or way of finding out) what to use or moreover, how to control it precisely enough. I figured that using a soldering iron to soften the plastic and push it away would work because I could more easily control the heat (more or less).

Unfortunately, the metal seems to have been extremely fragile (maybe it’s solder‽). Not only did the plastic warp a little bit and not soften easily to be pushed out of the way, but one of the lines even got a hole in it right through the metal.

Now I’m left with a ribbon cable (as seen below) and wondering how I can fix it. Is there a way to fix it as is or perhaps attach an extension?

Photo of damaged ribbon cable

  • @hit-and-run-downvoter Um, care to bother explaining the problem? – Synetech Oct 6 '12 at 19:10
  • Nothing to do with electronic design! Question should be closed. – Leon Heller Oct 6 '12 at 20:06
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    @LeonHeller, from the FAQ: We ask and answer questions about electrical and electronics engineering topics, which include electronics, … [not] consumer electronics such as media players, cell phones or smart phones, except when designing these products or modifying their electronics for other uses Would a question about etching a PCB be on-topic? If so, how is this not? Where do you purpose asking, a classified? Or maybe paying $500 for an electronics course to fix a $30 keyboard? This is a generic question that can apply to any and all ribbon-cable related issues. – Synetech Oct 6 '12 at 20:58
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    @LeonHeller - If this question isn't on topic here, then where? – Rocketmagnet Oct 6 '12 at 21:18
up vote 2 down vote accepted

I think this is the type of membrane keyboard where the metal is extremely thin. It's often not copper foil as you might expect, rather I think it's printed silver paste. Basically, it has no structural integrity of its own, relying on the plastic for that. If you rub away the surface of the metal, you quickly discover that the surface is all there is to it.

If your ribbon cable consists of two layers of plastic, with the tacks printed onto the inside surface of one, then you may have some success. Try to peel the two layers apart, and cut the non-track layer a few mm shorter.

Alternatively, you might try repairing the broken tracks with some wire glue.

Wire Glue

Follow the instructions on Repair the Keyboard Membrane.

  • Yes, it has two plastic layers, but I’m not sure how I could peel them apart without destroying the silver paste. I suppose I could try with an X-Acto knife… Thanks for the tip about the wire glue and the link; I figured this issue must have come up and been addressed before. – Synetech Oct 6 '12 at 21:02
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    I got a syringe of wire glue on eBay for $1.50 and used it to fix a couple of burnt traces on the plastic sheet from another keyboard. It didn’t conduct at all while wet, but once it was completely dry, it conducted with fairly low resistance. That keyboard is fixed; yay. I tried it on the edge of this question’s ribbon cable, but the traces are too small, so it’s difficult. I have an idea of a way to do it without shorting them. Either way, wire glue (or electrically-conductive adhesive) does work to fix a ribbon cable. Thanks. – Synetech Sep 18 '16 at 23:29
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    @Synetech - So glad you finally managed to fix it. Only 4 years later! – Rocketmagnet Sep 19 '16 at 20:25

There was an extended discussion on this in the home shop machinists forum a while back.

Answers ranged from "don't waste your time, replace the cable" to a half dozen ways to actually attempt to do so. My own take is that any repair is not going to be as reliable as outright replacement, but since/if you have nothing to lose, why not try?

  • But how could the cable be replaced? The lines are directly connected to the plastic sheet inside the keyboard. – Synetech Oct 6 '12 at 20:59
  • Well, if the cable truly cannot be replaced, I guess you have no choice but to either attempt a repair, or replace the entire keyboard. But since used keyboards are widely being given away (assuming you are in North America - ask on your local freecycle) I don't see that as being a problem. – mickeyf Oct 6 '12 at 21:03
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    It’s not a matter of replacing the keyboard (I already have one; that’s what I’m typing this on right now). It’s that this was my first wireless keyboard which I have grown extremely accustomed to, and having OCD, I can’t just throw it away, especially if there is any chance that it can be repaired (plus, it was part of a set with a mouse, so the receiver is sitting there with the F-Lock LED on and no way to turn it off which sticks in my brain like a dagger). – Synetech Oct 6 '12 at 21:06
  • Thanks for the link, there are some good suggestions in there that I’ll consider/try. – Synetech Oct 6 '12 at 21:06
  • @Syntech I have had, literally, a garage full of electronic and mechanical things that "had a chance of being repaired". After several decades, I'm finally getting rid of some (but only some!) of it. I feel your pain. – mickeyf Oct 7 '12 at 18:34

Thanks for this thread. I had a similar problem with an HP laptop. I'd taken it apart more that a few times, and the last time I assembled it the keyboard M key didn't work so I tried cleaning the ribbon cable; that didn't work. Then I used an eraser, thinking I was getting the dirt off the cable but in fact I was removing the contact area, and when I tried it again, none of my keys worked. What really worked well took about 5 min, and it's like new. Right at the edge of where the contact area starts I noticed a thin mylar top coating that I was able to peel back about 1/8 inch to the same width of the original, exposing brand new shiny silver contact area. I trimmed off the excess mylar I had peeled back and cut off the old contact area, giving me a new contact. Then I put four layers of scotch tape on the back of the contact to stiffen it and proved support and extra thickness. I carefully trimmed the scotch tape on the back to match the front. Plugged it in and it worked right off the bat with no need to jimmy or adjust, just like new.

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