100% conductive ink or similar solution?

Thread Starter

Bronxio

Joined Jun 7, 2020
13
Hi! I've got a fader that has a damaged track on its PCB. It should be 100% conductive (0Ω), but since some day, it is about 1,6kΩ. This fader is discontinued and can't find any dealer still selling it, so I'm trying to fix it.

I bought a conductive ink just to try, but failed (it has some resistance). Does anyone know about any solution for this? Attaching a cable to make a bridge is not possible (won't fit assembled). I attach a photo showing where I need to add the 0Ω bridge. It's about 6-7 cm.
 

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jpanhalt

Joined Jan 18, 2008
10,477
There are 2 types of conductive ink. One has conductive particles suspended in a matrix; the other precipitates pure silver (or other metal) nanoparticles onto the surface. The silver version is similar to Tollens reagent or "electroless" plating. (Electroless plating is also used for nickle,gold, and other metals.) The former is not solderable. The latter supposedly is; however, it is much more expensive unless you make the reagents yourself.

Do you have access to a chemistry lab?.
 

Externet

Joined Nov 29, 2005
1,544
Got into that problem at my manufacturing job; found the crimping at the ALPS brand faders were failing. Brought the ALPS big management shots to the factory to witness the failures. They said that would revise the crimping equipment on their production line.

Decided to implement a tiny amount of conductive silver ink applied seeping under the rivet to the carbon trace on the production line to out of the box new faders, to ensure ALPS future failures would never cause problems at our equipment production. Solved the issue.
1595515986467.png

1595516358321.png

A few rivets can be seen at this similar fader, but at the no-trace side. On your trace side picture, at the transition between the rivet and the trace, apply 1 mm of silver ink to bridge the gap under around the rivet. Let dry until next day. Silver ink was expensive but usage is minimal, worth it !
 

Thread Starter

Bronxio

Joined Jun 7, 2020
13
Wow, thanks for all your replies! Yes, I need a zero resistance solution. I think I'll try with the copper foil first. I've already tried with this silver ink, but failed (still too much resistance, doesn't work properly in the unit). I guess Externet used some more pure, as Jpanhalt suggested (I live in an island and I'm afraid that some of those reagents will be difficult to import because security reasons, but thanks!)

10K slide pots are common as I can see in Google, right; but this variation, not that common... with that thin trace from the center of a big one to a pin (the one that is failing, so the turntable fail finding exactly the center position). There is a lot with 3 pins, but not that much with 4.

I've seen this slide pot, but it isssss 10KM1, not 10KM2... Can't say if there is any functional difference. The seller offers only a 20€ shipping method and won't subtract the 24% VAT (not applied for my zone). It would be a little bit painful to find out that, finally, it doesn't work for the turntable
:D
I'll post here the results when I get some of that attractive Scotch tape and try.
 

jpanhalt

Joined Jan 18, 2008
10,477
I've already tried with this silver ink, but failed (still too much resistance, doesn't work properly in the unit). I guess Externet used some more pure, as Jpanhalt suggested (I live in an island and I'm afraid that some of those reagents will be difficult to import because security reasons, but thanks!)
Pure silver has a conductivity of 107% that of pure copper.

Silver and copper are the two most conductive metals known to mankind, with gold following behind in third place. The conductivity of silver clocks in at 63 x 10^6 siemens/meter, roughly seven percent higher than the conductivity of annealed copper, which stands at 59 x 10^6 siemens/meter.
You did not use the correct "silver" ink.

CLUE: eBay is not a reliable source for technical information.
 

Thread Starter

Bronxio

Joined Jun 7, 2020
13
How does this have both "zero resistance" and "10K ohms" at the same time?
Having a slide plot that has a trace with zero resistance (the thin one I've mentioned). I've measured a working unit several times and that's the resistance that this trace must have (0). As I've said, this 10K slide pot is a special variation for a specific system (and that's why it's difficult to find a replacement)

Jpanhalt, I appreciate all your info from all! The reason I've decided to try with copper is not conductivity, but price. I knew that ink I've bought was risky, but 154€ is too much for my case: I'm just trying to save a working turntable (I could buy a new one with minimum requirements from 159€), that's why I'm grateful for knowing more than one solution (even if it's not ideal)
 
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jpanhalt

Joined Jan 18, 2008
10,477
If it's a resistive or carbon trace you cannot solder to it. So, what's it worth to you working versus trash?

158 € is too expensive. The principle component is silver nitrate. Hard to believe that can't be shipped to your island. Did you look for electroless plating? Nickle, tin ,silver, gold, virtually any metal will be better than silver colored paint.
 

Reloadron

Joined Jan 15, 2015
5,667
This is your original image. Can you mark up the break? Yes, it has 4 terminals but the only two I see close to zero ohms would be the two terminals on the bottom of the image.

4 wire slide pot.png

There will always be some resistance, there is no zero ohms, a fractional part of an ohm yes but no zero. Can you mark up the image to reflect where you want this zero ohms?

Ron
 

Externet

Joined Nov 29, 2005
1,544
Translating the above : Where in the carbon traces is continuity lost ? At a rivet or somewhere along the trace ?.

If somewhere along a carbon trace; when all attempts fail, use a soft pencil to deposit some carbon...
 

Thread Starter

Bronxio

Joined Jun 7, 2020
13
There will always be some resistance, there is no zero ohms
That's right, I think it's not actually real, absolute 0Ω; I guess (and I hope!) the main unit has a threshold to "understand" it where the stem is in the center (my measuring was in kΩ)

Where in the carbon traces is continuity lost ? At a rivet or somewhere along the trace ?
somewhere along the trace. The rivets seem to be fine.

I have a total of three units: one in good working condition and two faulty ones. I've recorded the first time I opened them (now they are soldered, because I wanted to test them in the turntable). Here you have the measuring of one of the faulty ones on this YouTube video. As you can see, it seems that in some specific part is the problem. Honestly, can't say why it happens, but other users had the same problem as well with this turntable model: the main unit doesn't detect the center in the real center, and because the Externet experience, I've confirmed that Alps doesn't seem to do durable slide pots.

This photo is the one with 1.6kΩ (the same as the one in the video). It's marked like this:

  1. Green: 0~10.67 (depending on the stem position). All my units do this, no problem.
  2. Blue: the trace that I've measured 0kΩ in the working unit, and >0kΩ in the faulty ones (the copper foil will be here)
  3. Red: the good one is 5.32kΩ (fixed value, no matter where the stem is); the faulty ones, >5.32kΩ

vlcsnap-2020-07-24-23h12m15s889.jpg

I guess that thin trace is just supposed to "cheat" the half resistance of the whole big trace that is connected to.
 

Externet

Joined Nov 29, 2005
1,544
Slide the two probes of a ohmmeter a couple of millimetres apart along each trace to find if there is a crack or gap somewhere.
 
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