Yellow Glue strikes again

Is that hot melt glue or something else? Hot melt should, umm... melt, not burn.

"Jeff Liebermann"

.... Phil

No, this crap looks like 3M weather strip adhesive. Sometimes it looks like it's applied sparingly, other times it looks like it was put on with a caulking gun.

Jeff

"Jeffrey Angus"

At first impression, it looks like ordinary contact adhesive - but it is quick setting and dries to a hard surface. With time and heat it become tan coloured and brittle. Then it goes toast brown and becomes corrosive and conductive.

If coating the pins of an op-amp, the leakage current causes DC offsets and crackling noises.

If coating small diodes and resistors etc - it will slowly eat the leads right off.

If coating PCB tracks with hundreds of volts between them, the conduction heats the glue directly until there is an explosion.

IME , a local ambient temp of about 55C is enough to set it off on its pathway to hell.

.... Phil

Just answer the question. I've seen plenty of hot melt glue being used. It comes in clear, yellow, and brown. I've never noticed anything else. Maybe it's a pro-audio only thing? I don't do any pro-audio as what little audio repair work I do usually doesn't involve incinerated parts and carbonized yellow glue.

It's probably related to that crap rubber they love to use for drive belts and such that turns to extremely sticky goo that's next to impossible to clean off of everything it touches.

Jeff

"Jeff Liebermann"

Always Asian made gear, from about the 1980s onwards.

TV sets, VCRs, SMPSs anything where the maker felt it was a good idea to glue things to the PCB.

Do a Google search on this NG under " yellow glue".

..... Phil

I had an M1 with exactly the same problem. Conductive gak all over the place, very messy, but fortunately didn't blow anything up.

Gareth.

If the brown hard-glue is the same as the yellow stuff. Is the progress to destruction that it becomes hygroscopic going from yellow to brown and so becomes conductive for CMOSSy sort of stuff but if HV around then conducts enough to then carbonise and become ever more conductive?

that stuff is pure s*it.

The rumor among techs in the U.S. when this stuff first showed up was it was originally manufactured by Sony and it was known as "Sony glue". Don't know if there was any truth to this or not. As Phil said, it was in widespread use, for example: Mitsubishi televisions, Adcom preamps and tuners, Yamaha receivers, Extron products and many others which I can't recall off the top of my head. Chuck

The brown brittle stuff I scraped off the M1 PCB was around the low voltage audio pre-amp and Power Amp IC. It was conductive enough to render the circuit useless, no HV necessary.

Gareth.

"Gareth Magennis" wrote in news:Ixl7q.182412$ snipped-for-privacy@newsfe27.ams:

the manufacturers probably don't get the products back(due to their age) for failure analysis,and thus are unaware it happens. No "closed-loop action process".

OR,it's planned "obsolesence". or both. ;-)

going

As long as it lasts through the warranty, they don't care.

Yup been there in the past 30 some years. Lots of Chinese VCR SMPS. I reckon that crap is a moisture trap that eventually leads to the demise of chokes, coils etc..

"Alien"

The worst problems are always with gear that runs 24/7.

No chance for moisture ingress there.

.... Phil

Another miscreant is some formulation of conformal coating that over 20 or

is

had

lue

had

=A0going

Sony had a problem with this glue on broadcast video recorders years ago. Their tech bulletin blamed "CHLOROPRENE GLUE". One current mfr data sheet shows a reduction in resistance from 10^13 to 10^8 after