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 ****ty 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/

That brown glue stuff
 

"N_Cook" wrote in message
...
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 ****ty 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?

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.

That brown glue stuff
 

On Jul 13, 8:42 am, "N_Cook" wrote:
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 ****ty brown stuff
on the other.

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

That brown glue stuff
 

junebug1701 wrote in message
...
On Jul 13, 8:42 am, "N_Cook" wrote:
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 ****ty brown
stuff
on the other.

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

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
http://home.graffiti.net/diverse:graffiti.net/