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That brown glue stuff

Used for fixing otherwise floppy bits to boards. Is it hygroscopic ? whatever the word is, but pulls dampness out of the air. Beocenter 4000 from 1985 with the LC7815 (not V reg) electronic 2 pole 4 way switch, internally locked into Aux only input, so disabling everything else.

0.7 inch pitch 28 pin DIP but now removed and replacement available. Affected input was on one side of the IC and some of this shitty brown stuff on the other. But now removed , the 2 glued pins are almost corroded through but not obvious before removing the IC, and have presumably conducted moisture, capillary fashion, into the IC. So will remove that glue and another dollop near another IC. Will hot-melt glue go the same way after a qurter of a centuary. Is it bulking filler in these glues that cause the problems ? I have used talcum powder to bulk out on occassions but could that be problematic in future , so a better choice? 
--
Diverse Devices, Southampton, England 
electronic hints and repair briefs , schematics/manuals list on 
http://home.graffiti.net/diverse:graffiti.net/
Reply to
N_Cook
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The brown glue that usually causes the problems you describe normally becomes very brittle and chips off easily.

If something really does need tacking down I'd use a very small spot of superglue or a blob of 2-part epoxy, for larger components that need support but need to flex with thermal expansion silicone RTV is a good choice, instant gasket is sometimes cheaper from auto accessories stores, or if you use a lot of it a tube of RTV for a "mastic gun" from a builders yard usually works out cheapest.

Reply to
ian field

Nigel, from my experience this brown glue eventually turns dark brown, and when it does it becomes conductive. I have found it difficult to remove. A plastic serrated knife like you might find in a take-away food box works well and is soft enough not to damage the traces on the board. I really hate that glue.

James

Reply to
junebug1701

air.

way

else.

stuff

On first sighting of this latest case, I tested the glue and it was more than 30 Megs , just retested a bit and over 500 megs.

I suspect the plain gummy petroleum glue is ok over time, but it is a problem with a filler/bulking agent used. I agree it goes brown with age, perhaps it is something like corn flour or vegetative starch as filler. I doubt a mineral like talcum or French chalk, as a filler, would go this very dark brown or be a problem. The recent failure was due to corrossion localised to where this glue had glooped over a few pins. Those pins looked ok but after removal I could see corrosion and one of the pins, without the pcb support, has almost sheared off due to the underlying corrosion.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

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