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PCB Repair - Newby Question(s)

torontobob

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Hi All.

Where to start ... I've done tons of point-to-point stuff over the last 50 years. (Just finished reassembling a Hammond B3) (150+ solder joints!) But now I have a PCB issue to tackle - and that's new/scary to me. It's the main-board of a 80's Korg PolySix synthesizer which has a sadly common issue - an on-board battery leak that destroys PCB traces and some components. If you check the photo you can see the sad situation. Anyway, there is a marvelous resource here - http://www.oldcrows.net/~oldcrow/synth/korg/polysix/repair.html - and that's the road I'm looking at going down. (Carefully!) However, that document/site is 20+ years old and I'm wondering about a couple of things:

  • The repair wire used to replace the traces - not specifically mentioned - but would 30awg wire be appropriate?
  • In my searches I've run across repair procedures that use a conductive pen instead. Is that a more "modern" approach? Or is it for specific circumstances that may or may not apply here?

I'd love to hear any comments/suggestions you all may have.

Thanks!

Bob
 

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c_mitra

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Conductive ink would be simpler to use. You need to clean the board thoroughly and use the conductive ink.

Remove the battery and solder two wires and get a separate battery holder connected.

Use a magnifying glass and a pen light torch and a multimeter to see which connections are dead.

it will take time but it is worth it.

150 solder joints are low-count and you are lucky!
 

BradtheRad

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Years ago I purchased the Circuitworks silver conductive pen and epoxy. Just right for materials that are hard to solder. Example, connect wires to solar cells. Fix conductive traces on a car window.

Local auto parts stores carry a grid repair kit for car windows. Examine several kits because some have dried out copper liquid.

Internet articles tell how to make a home-brew mixture with graphite powder.
 

torontobob

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Conductive ink would be simpler to use. You need to clean the board thoroughly and use the conductive ink.

Remove the battery and solder two wires and get a separate battery holder connected.

Use a magnifying glass and a pen light torch and a multimeter to see which connections are dead.

it will take time but it is worth it.

150 solder joints are low-count and you are lucky!
Thanks so much!

Ok, so the ink is the way to go. I was kind of hoping that would be the answer. And yes - multimeter to check the traces. (Still missing my father's Simpson 360 my brother snagged 30+ years ago. But I have a couple of good ones.)

Question: Which conductive ink would you recommend?
 

c_mitra

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Most common ones are silver colloid based, with a plastic binder and they get dried up very fast. You do not have many choice: but avoid graphite based ones (they look, you guessed it, black) because they are stable but not really good for high current. If your traces are small signal (from the photo they appear so) then you can use any one that are readily or locally available. Do not try to overdo it (you may short adjacent tracks) but if you wish you can apply twice (it is only a paint) but must be very careful (apply second coat only after the first coat is dry- about 15 mins or so).
 

c_mitra

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I would prefer the silver paint based one but they cost a lot!

You would not be able to use them after some time, they dry out fast (they are mostly amyl acetate solvent based).

I have not seen before Ni based conducting ink; they are rather new.

Out of 8gm of ink you may be using only 100mg or less.

But a conducting paint based pen is simplest for the present task.

If you short a pin (perhaps applied too much of it), you can clean up with a cotton bud dipped in acetone. You need to repeat the cleaning several times (because a thin film, almost invisible, often stays and can be nuisance to detect later) with fresh cotton buds dipped in fresh acetone.

Good luck!
 

FvM

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I wonder if any of the conductive pens is fine enough to repair traces on the shown board. Personally I'd absolutely prefer to substitute broken traces by thin copper wires. Another point to consider, epoxy IC packages are not fully hermetic, electrolyte may have entered and cause malfunction.
 

KlausST

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Hi,

I have no experience with conductive pens.
My idea also was a thin wire.
--> Do a search for "VEROWIRE"

The wires may be fixed (after soldering) with glue or lacquer

Klaus
 

Externet

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Absolutely backing the opinion to re-create traces by using copper wire and not silver ink for this repair.

By the way; had to replace one of those 3.6V backup Ni-Cd batteries in the spectrum analyzer once. I used a 18650 lithium-ion cell instead. Just make sure charging voltage the circuit applies is ~4V and not more.
 

c_mitra

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I wonder if any of the conductive pens is fine enough to repair traces on the shown board. Personally I'd absolutely prefer to substitute broken traces by thin copper wires. Another point to consider, epoxy IC packages are not fully hermetic, electrolyte may have entered and cause malfunction.
These pens are felt-tipped with a typical middle size line width; I have used them long time back. More recently we used silver paste for electrical connections we did not wish to take the risk of high temp. I used a fine brush to make signal connections and thick brush for power connections. Once we baked it at 120-150C it was a very good conductor (could not be measured with a regular multimeter) but lacks flexibility. The paste we bought has 60% solid with 40% silver content. The solvent was nitromethane and amyl acetate.
 

barry

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One more vote for wire. It's cheap, available and reliable. You don't have to deal with baking or scary-sounding chemicals. Wires are used in military and space applications all the time. If it's good enough for spacecraft, it's good enough for your synth.

And I would also think that wires will stand up to vibration better than paint, especially if you really pound on your keyboard (or drop it on your way to a gig.)
 

Relayer

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Hello Bob,
I would highly recommend you use some white viniger soaked into a used toothbrush to neutralize the acid from the backup battery spill. Then clean it with isopropyl alcohol to remove the rest of the viniger.
Use Kynar wire for your trace replacements. If you're in Australia, you can buy the wire from Wiltronics. It's 30AWG sized wire coated in insulation.
If you live elsewhere, it shouldn't be difficult to obtain. Just do a Google search.
If you find that you need to attach a wire to an IC lead, then obtain a fiberglass pen to remove the corrosion. Once again, do a google search on it. A fiberglass pen is excellent in cleaning up solder joints for resoldering as well.
If you do all the work and it still doesn't function properly, you may have to remove some IC's to see if any traces underneath have been compromised.
Good luck on this endeavor and please keep us posted on your progress.
Regards,
Relayer
 
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c_mitra

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Hello Bob,
I would highly recommend you use some white viniger soaked into a used toothbrush to neutralize the acid from the backup battery spill. Then clean it with isopropyl alcohol to remove the rest of the viniger.
Bad recommendation and must not be followed for cleaning electronic items.

I do not know where you received this information.

Vinegar is an acid- diluted acetic acid and it cannot neutralize the acid from backup battery.

Vinegar is also corrosive. Never use vinegar for (cleaning) electronic items.

By the way, common nickel cadmium cells do not use or contain acid. The alkali attacks tin very rapidly and lead more slowly.

Save your vinegar for your salads.
 

Relayer

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Save your vinegar for your salads.

Smart arse.

I do not know where you received this information.

From a reputable pinball machine repairer in the States.
Joe's Classic Video Games. Look it up. He's been in the business for years.

By the way, I doubt very much you've ever repaired a thing in your life. You're all "theory" and
nothing else.

Relayer
 

barry

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Hello Bob,
I would highly recommend you use some white viniger soaked into a used toothbrush to neutralize the acid from the backup battery spill. Then clean it with isopropyl alcohol to remove the rest of the viniger.
Use Kynar wire for your trace replacements. If you're in Australia, you can buy the wire from Wiltronics. It's 30AWG sized wire coated in insulation.
If you live elsewhere, it shouldn't be difficult to obtain. Just do a Google search.
If you find that you need to attach a wire to an IC lead, then obtain a fiberglass pen to remove the corrosion. Once again, do a google search on it. A fiberglass pen is excellent in cleaning up solder joints for resoldering as well.
If you do all the work and it still doesn't function properly, you may have to remove some IC's to see if any traces underneath have been compromised.
Good luck on this endeavor and please keep us posted on your progress.
Regards,
Relayer
Um, you cant neutralize acid with another acid.
 

Relayer

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Um, you cant neutralize acid with another acid.

You can if you're trying to neutralize alkaline contaminants.
The vinegar is temporarily used to neutralize and clean up any alkaline on the exposed metal.
It's not on long enough for it to start eating anything away.
Regards,
Relayer
 

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