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Old 4th January 2008, 01:17 AM   #1
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Default Circuit board repair suggestions?

I've got a good sized 110W x 2 stereo integrated Yamaha amp, I forget the model number off the top of my head. Well it's having problems. Looks like maybe a cat got sick on the top of the case or possibly something was spilled right over the rectifier. What ever it was has long since dried but must be causing a very small short over long periods and has now crisped the board a bit between the legs of the rectifier. Is there something I can put on it to stop the shorting? I was thinking the paint on electrical tape stuff or maybe some 30 minute epoxy? Clear enamel nail polish? Maybe there is a product made just for this?

Thanks,
Bryan
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Old 4th January 2008, 01:27 AM   #2
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Epoxy is the best thing. they make circuit board repair kits with colored epoxy. but the normal stuff from the hardware store is the same thing without the color. Apply in layers and let dry in between.

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Old 4th January 2008, 01:27 AM   #3
Tolik is offline Tolik  Israel
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Generally PCB can be cleaned with any strong thiner. Try to use small amount first to determinate if your cleaning liquid not gamaging silk screen of the board.

To prevent short sirquit in future - epoxy the best choise.
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Old 4th January 2008, 04:51 AM   #4
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It was shorting very badly. I used some aerosol contact / electrical cleaner on it and compressed air and now it's just a small sizzle. I have some 30 minute epoxy here, I'll try that and see how it goes.

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Bryan
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Old 4th January 2008, 05:13 AM   #5
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Things that arc generally create a carbon track, and they'll continue to arc until you remove it. Sometimes scraping with a knife is sufficient, sometimes you have to use a burr in a rotary tool and cut right into the fiberglass. In any case, 30 minute epoxy is a good choice. Avoid 5 minute epoxy as the properties of the stuff are pretty poor. Krylon clear plastic spray is also a good coating for circuit boards, and you can easily repair through it.
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Old 4th January 2008, 09:48 AM   #6
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My guess it that it is an older Yamaha with a tan-colored paper-epoxy board.

The rectifiers cooked the board in the normal course of events anyway.

You must scrape all the dis-coloration off, even if you go completely through the board.
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Old 7th January 2008, 06:32 AM   #7
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It's late 80's, Green PCB I think, it's not near the puter and I don't remember off the top of my head. It's also a single large bridge rectifier, raised off the board about a half inch. Doesn't seem to have cooked the board, it was just burnt a bit where it has shorted due to what ever was spilled / barfed (cat?) on it.

After I had cleaned it with cleaner and compressed air the air must have been damp and I think that left enough residual moisture on the board to sizzle a bit when I tried it out right after cleaning. After sitting a few days I tried it again around the same time I posted this and it didn't short at all. I coated everything down there with a coat of 30 minute epoxy for good measure and I think it'll be fine now.

Thanks for everyones help,
Bryan
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Old 7th January 2008, 07:21 AM   #8
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carbon tracks burned into the board are not common, but they do happen, even on green fiberglass boards. easiest fix is to scrape it off with an xacto knife. you have to scrape until you get under the track. if it goes more than 1/2 way through the board, use epoxy cement as a filler. if its a fiberglass board, put a drop of water on the board while scraping, it will keep the fiberglass dust from getting all over your fingers (which can cause a painful and invisible splinter if a fiber gets embedded in your skin).
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