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  • Thumb Clip Pull
    replied
    Hard, clear coat.

    Hi Mike,

    No. I believe that the clear coating is hard and clear. It is not very thick. I think that it is just a protective coating that was appied when the board was originally manufactured.

    I think that the board was sprayed with this black coating. Then it looks like two capasitors and a piece of wire were soldered to the board. One can style capasitor was soldered to the component side, one flat waffer style capasitor and a thin piece of wire were soldered to the reverse side. The capasitor and the wire on the reverse side were spray painted with this black stuff. The capasitor on the front side was left unsprayed.

    I don't believe that the spary was done at a factory, because it is not done very well. (Some of the other components were not completely covered, and some areas are thicker than other areas.)

    As to the clear coming off before the black. I spread a little stripper on the corner of the back side of the circuit board with a soft bristle acid brush. I let it sit for a little while, checking back very often. I took a pen knife and scratched at it a little when I noticed nothing was happening. I spread on a little more stripper and waited a little longer. I noticed that a little of the coating was breaking up. I could push it around a little bit with the acid brush. Then I noticed that one of the solder runs was exposed in places and still covered in others. I scratched at this gently and was able to remove some of the black but not all of the clear.

    Some of the stripper ran over the edge of the board and crawled up the component side of the board. I pushed the clear and black coating off easily because it had been on the surface longer. I found the original white markings in the corner of the printed circuit board. The white was begining to come off. I used some tap water on a cloth to clean off the rest of the stripper and stop the stripping action.

    I dried the board and examined it closely. It looks as it the board is stripped right down to the fiber that it is made of. There is no glossy finish at all. It may have been a trick of the light, but I got the impression that perhaps the board material was begining to swell. ( I could be wrong on that one.)

    I have set the whole thing aside for now. I will have to do some research on what the black coating may have been and what will strip it off.

    Yours,
    Thumb Clip Pull Pin.

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  • Mike W
    replied
    I was thinking party time. I had a circuit board that had the soft rubber like potting on it. I soaked it in a can of acetone over night and I was able to remove it. It didn't hurt the markings on the components. It is strange that the stripper is working on the clear and not the black on top of it. Is the clear rather soft so that you can pry it loose from the board?

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  • Thumb Clip Pull
    started a topic Stripper update!

    Stripper update!

    For the entertainment of several...

    I tried using a little bit of paint stripper on one corner of the back side of the black painted circuit board from my Miller Syncrowave 300 welder. Unfortunately the stripper did not have much effect on the black coating, but it did desolve the "clear coat" under the black paint. I was able to remove small sections of the clear coat and the black substance in tiny scales. However, I think that this may also remove the markings on the board and the color bands and such on the components. This particular stripper may also de-laminate the printed circuit board itself!

    I think that the next logical step would be to find out if there are solvents especially formulated for removing "black conformal coatings". I remember learning that conformal coatings are used to protect circuit components on circuit boards in the Marine Corps years ago. However, we learned how to remove clear coating on component solder joints and circuit board runs. We never considered removing component masking coatings on a large scale.

    We were also taught to clean the board very well and recoat the repair site with the same or simular coating.

    Yours,
    Thumb Clip Pull Pin.
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