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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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  #1  
Old 09-21-2009, 06:46 PM
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Default How do you remove acid corrosion from pcb with components?

Hi everybody! I am VERY new and self-teaching myself. Be gentle!

I have found a few little gizmos that do dot work because the batteries have been leaking for several years. (AA 1.5V Alkaline, Pile Alcaline)

The challenge for me is to repair them if nothing else for the "Cool I am learning this stuff" factor.

Is there a liquid you guys use to possibly brush on a PCB board WITH components (trimmers, resistors, diodes) that will eat the corrosion but not damage the components then blow off with compressed air (possibly)?

In particular----there is this one trimmer that I know i will not be able to replace because I believe it was custom made into a side thumb wheel. It is supposed to be a 5k trimmer but it is reading 5-15 MEGA-Ω due to the resistance the corrosion is causing.

Corrosion will cause increased resistance right?

Thanks and "HI!" to all.

There is so much to learn that is WAYYYYY over my head.

Also, I need a referral to a tutorial on how to turn a schematic into a working circuit or project.

I know all the symbols and understand the concepts but I'm having difficulty figuring out the order of flow especially when 2 or more components appear to be connected wih each other as to not blow something.

I hope it is okay that I "Hi-Jacked" my own thread!
Sean
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Old 09-21-2009, 08:22 PM
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Fairy Liquid, a toothbrush, warm water and elbow grease work wonders.

Allow the equipment to drain and air dry thoroughly afterwards 1- 2 days.

Corrosion will not increase the resistance of any component connected in parallel to the corrosion. So the resistance of your pot will only increase if the corrosion is causing bad contact between the wiper and the track. the track should remain at 5k.

Good experimenting with your new hobby.
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Old 09-21-2009, 08:40 PM
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What is "Fairy Liquid?" My guess is that is a general surfactant, like 409 Cleaner in the USA. Be sure to rinse well with water afterward. If you want to speed drying, rinse with 50% or so isopropyl alcohol, then pure isopropyl alcohol. The intermediate step helps to dissolve the water.

You can remove corrosion, but that will not renew the surface that is left.

As for circuit building, look up "schematic capture." Bill Marsden on this forum has some nice hints in his blogs. Another term to look up is bread boarding.

John
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Old 09-21-2009, 09:08 PM
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"Fairy liquid"? for a bit I thought I was being poked fun at!

409 in a spray bottle? For real? When I was a kid i set a bottle on the hood of my parents car and it ate the paint. Wouldnt that ruin all the markings on a PCB

I was hoping for something like jewlery cleaner that would leave things nice and polished like when you pur Coca-Cola on the terminals of a car battery.

Hey John,
Thats the problem Ive been bread boarding but I cant tell from schematics the "trace" for lack of better description of the flow in case "multi- connected components" have to before or after.

I read a thread http://www.allaboutcircuits.com/vol_1/chpt_7/3.html on making copmlicated circuts with resistors and caps on here make sence buuuut I NEVER would have gotten what they got. That would mean "it wouldnt work!"

Are you telling me to just "google it"
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Old 09-21-2009, 09:15 PM
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I think that Dawn dishwashing detergent is the USA equivalent of the UK's "Fairy Liquid"
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Old 09-21-2009, 09:24 PM
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Yes it's washing up liquid.

The industrial equivalent is called 'Teepol'.

I recommend patience, rather than alcohol. Water can get inside many things and thin films will not be displaced by alcohol if held by surface tension.
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Old 09-21-2009, 09:32 PM
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Okay so I was being poked fun at........ DISHWASHING LIQUID does NOT remove oxidation!

Corrosion IS OXIDATION!

Corrosion involves the deterioration of a material as it reacts with its environment. Corrosion is the primary means by which metals deteriorate. Corrosion literally consumes the material reducing load carrying capability and causing stress concentrations. Corrosion is often a major part of maintenance cost and corrosion prevention is vital in many designs. Corrosion is not expressed in terms of a design property value like other properties but rather in more qualitative terms such as a material is immune, resistant, susceptible or very susceptible to corrosion.

The corrosion process is usually electrochemical in nature, having the essential features of a battery.

Corrosion involve two chemical processes…oxidation and reduction. Oxidation is the process of stripping electrons from an atom and reduction occurs when an electron is added to an atom. The oxidation process takes place at an area known as the anode. At the anode, positively charged atoms leave the solid surface and enter into an electrolyte as ions. The ions leave their corresponding negative charge in the form of electrons in the metal which travel to the location of the cathode through a conductive path. At the cathode, the corresponding reduction reaction takes place and consumes the free electrons.




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Old 09-21-2009, 09:36 PM
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Quote:
Originally Posted by bigcape View Post
"Fairy liquid"? for a bit I thought I was being poked fun at!

409 in a spray bottle? For real? When I was a kid i set a bottle on the hood of my parents car and it ate the paint. Wouldnt that ruin all the markings on a PCB
409 and the original Fantastic appear to be ethylene glycol-type cleaners. They may have methyl ether modifications (e.g., glyme) to help dissolve oils and greases, and they have added surfactants. They are not particularly strong solvents, and they will not affect cured enamel paints with short exposure times. They will not remove the markings on a PCB. Frankly, I would just go with pure water or water with a little detergent (few drops per 6 oz.) Dawn is fine; I would use Cheer Free...I don't like the smell of Dawn.

Quote:
I was hoping for something like jewlery cleaner that would leave things nice and polished like when you pur Coca-Cola on the terminals of a car battery.
Some jewelry cleaner is ammoniated; older cleaners contained cyanide. The cyanide was a great cleaner, but was bad for depressed jewelers. Their purpose, though, is quite different from removing corrosion and salt deposits from old batteries.

Quote:
Hey John,
Thats the problem Ive been bread boarding but I cant tell from schematics the "trace" for lack of better description of the flow in case "multi- connected components" have to before or after.
I don't understand that question.

Quote:
Are you telling me to just "google it"
Not at all. Google is just an alternative. As I mentioned, Bill Marsden and AAC provide many helpful resources here.

Do you want to convert schematics to PCBs?

If so, that is where schematic capture comes into play. I use Eagle, which is available as a free version.

John
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Old 09-21-2009, 09:47 PM
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While you are correct that
Quote:
DISHWASHING LIQUID does NOT remove oxidation
you might note that
Quote:
a toothbrush, warm water and elbow grease work wonders
The scrubbing is effective. More so when you add some baking soda as an abrasive and acid neutralizer.

Removing crud takes some effort. The copper traces and component leads that have corroded away do not come back, so removing the corrosion does not necessarily restore the circuit.

You may be able to see it clearly enough to make a schematic, though.
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Old 09-21-2009, 09:54 PM
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Quote:
Originally Posted by beenthere View Post
While you are correct that you might note that The scrubbing is effective. More so when you add some baking soda as an abrasive and acid neutralizer.

Removing crud takes some effort. The copper traces and component leads that have corroded away do not come back, so removing the corrosion does not necessarily restore the circuit.

You may be able to see it clearly enough to make a schematic, though.
The copper traces are in good shape its some of the wires and pots that are bad.

A corroded wire WILL have much higher resistance for certain!

Just like with an OXIDIZED soldering tip you will burn up the component BEFORE the solder melts!

I cant do any repairs untill I get the crap off!

Also, what gets the epoxy stuff off to even get to some of the solder welds?
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