Is it possible to run a patch wire here?

kelvinhall05

12 Feb 2020, 00:21

The pads were scraped away by...something, not sure what. The top one doesn't have a connection between both sides. This set of pads was used to tell the typewriter this keyboard is from that the case was open and probably to disable the keyboard, but I'm not sure if it was a digital or physical cutoff, so it may be necessary for the keyboard to function. Anyway, I was wondering if I can run patch wires to fix the top pad and bridge the top and bottom pad. Thanks!
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frogmaster

12 Feb 2020, 14:34

I would use something like "Copper Foil Tape with Conductive Adhesive" from adafruit or equivalent, cut into appropriate shape. Or barring that, regular copper foil with small dabs of conductive paint where copper meets the membrane trace, as regular foil doesn't have conductive adhesive.

kelvinhall05

12 Feb 2020, 15:40

frogmaster wrote:
12 Feb 2020, 14:34
I would use something like "Copper Foil Tape with Conductive Adhesive" from adafruit or equivalent, cut into appropriate shape. Or barring that, regular copper foil with small dabs of conductive paint where copper meets the membrane trace, as regular foil doesn't have conductive adhesive.
How much does something like that cost? I'm also wondering because I couldn't seem to get any conductivity from the wire, even in a section that isn't broken or scratched away. Is there some mask or something that has to be removed first?

frogmaster

12 Feb 2020, 20:22

kelvinhall05 wrote:
12 Feb 2020, 15:40
How much does something like that cost? I'm also wondering because I couldn't seem to get any conductivity from the wire, even in a section that isn't broken or scratched away. Is there some mask or something that has to be removed first?
Couple of € from aliexpress or other usual suspects, more from reputable places, depends on the width of the tape... It looks like there is a mask, so yes, that needs some careful scraping, i would use exactoknife and much care. Maybe fiberglass brush would be better, but i have no experiences with those.

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Willy4876

13 Feb 2020, 01:01

If you just want to connect the two sides then yes you absolutely can run a wire. I would go about it by scraping off the solder mask (the green non-conductive coating over the traces) from the traces on either side of the damaged pad. Then you could just run a wire between the two new 'pads' that you created. Depending on the trace width this can be hard, but I have done it in the past at work. I am not sure that this would fix the key, however. That would depend on whether there is enough of the damaged pad to conduct between the two sides.

You could also look into conductive paint but I have no experience with that.

kelvinhall05

13 Feb 2020, 03:19

Willy4876 wrote:
13 Feb 2020, 01:01
If you just want to connect the two sides then yes you absolutely can run a wire. I would go about it by scraping off the solder mask (the green non-conductive coating over the traces) from the traces on either side of the damaged pad. Then you could just run a wire between the two new 'pads' that you created. Depending on the trace width this can be hard, but I have done it in the past at work. I am not sure that this would fix the key, however. That would depend on whether there is enough of the damaged pad to conduct between the two sides.

You could also look into conductive paint but I have no experience with that.
frogmaster wrote:
12 Feb 2020, 20:22
kelvinhall05 wrote:
12 Feb 2020, 15:40
How much does something like that cost? I'm also wondering because I couldn't seem to get any conductivity from the wire, even in a section that isn't broken or scratched away. Is there some mask or something that has to be removed first?
Couple of € from aliexpress or other usual suspects, more from reputable places, depends on the width of the tape... It looks like there is a mask, so yes, that needs some careful scraping, i would use exactoknife and much care. Maybe fiberglass brush would be better, but i have no experiences with those.
Tried scraping, either I scrape too much or too little. Any way to chemically remove it?

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Willy4876

13 Feb 2020, 18:18

This thread has a couple of ideas that you could try. I haven't tried any of them so be careful. I think like their idea of using high grit sand paper but I'm not sure how precise it would be. You could also try an emery board (the thing for polishing your nails) they're pretty cheap, high grit and you don't have to buy a ton of them at once.

In the defcon video on that page the part about removing solder mask starts ~13:25.

https://www.eevblog.com/forum/beginners ... oldermask/

kelvinhall05

14 Feb 2020, 00:11

Willy4876 wrote:
13 Feb 2020, 18:18
This thread has a couple of ideas that you could try. I haven't tried any of them so be careful. I think like their idea of using high grit sand paper but I'm not sure how precise it would be. You could also try an emery board (the thing for polishing your nails) they're pretty cheap, high grit and you don't have to buy a ton of them at once.

In the defcon video on that page the part about removing solder mask starts ~13:25.

https://www.eevblog.com/forum/beginners ... oldermask/
So I looked into this a bit more, and it seems that conductive paint is the way to go, but what I just don't understand is how to remove the damn solder mask. I've tried scraping with half a dozen different knives, xactos, screwdrivers, etc, and it just seems like there's a point where you're either removing the coating, or the trace, there doesn't seem to be an in-between. I'm assuming that just painting some concuctive ink/paint onto the plastic-y coating stuff won't work, right?

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Polecat

14 Feb 2020, 03:55

kelvinhall05 wrote:
14 Feb 2020, 00:11

So I looked into this a bit more, and it seems that conductive paint is the way to go, but what I just don't understand is how to remove the damn solder mask. I've tried scraping with half a dozen different knives, xactos, screwdrivers, etc, and it just seems like there's a point where you're either removing the coating, or the trace, there doesn't seem to be an in-between. I'm assuming that just painting some concuctive ink/paint onto the plastic-y coating stuff won't work, right?
Try a pocket knife with a curved tip blade (like a Swiss Army knife). Doesn't have to be sharp, in fact dull may work better for this. Or try some fine sandpaper or emory cloth. It's not hard, at least after you've done it a couple hundred times.

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Willy4876

14 Feb 2020, 03:57

kelvinhall05 wrote:
14 Feb 2020, 00:11

So I looked into this a bit more, and it seems that conductive paint is the way to go, but what I just don't understand is how to remove the damn solder mask. I've tried scraping with half a dozen different knives, xactos, screwdrivers, etc, and it just seems like there's a point where you're either removing the coating, or the trace, there doesn't seem to be an in-between. I'm assuming that just painting some concuctive ink/paint onto the plastic-y coating stuff won't work, right?
I haven't used it so I can't advice you on that but I'd look for a youtube video on the topic and see what people say.

kelvinhall05

15 Feb 2020, 22:05

Willy4876 wrote:
14 Feb 2020, 03:57
kelvinhall05 wrote:
14 Feb 2020, 00:11

So I looked into this a bit more, and it seems that conductive paint is the way to go, but what I just don't understand is how to remove the damn solder mask. I've tried scraping with half a dozen different knives, xactos, screwdrivers, etc, and it just seems like there's a point where you're either removing the coating, or the trace, there doesn't seem to be an in-between. I'm assuming that just painting some concuctive ink/paint onto the plastic-y coating stuff won't work, right?
I haven't used it so I can't advice you on that but I'd look for a youtube video on the topic and see what people say.
Bit of an update. Bought a cheapo nail file, and spent like 10 minutes tediously filing, and then I bridged with tape and aluminum foil, and it works!

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Willy4876

Yesterday, 02:20

I am glad to hear that you got it working!

kelvinhall05

Yesterday, 03:22

Willy4876 wrote:
Yesterday, 02:20
I am glad to hear that you got it working!
Yeah, now I just gotta map the damn matrix :(

That'll take a while lol. Kind of a complicated matrix.

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