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Yellow Glue strikes again

** I had hoped that the dreaded Yellow Glue peril had gone away - but it is still with us.

Most of you will have seen it holding parts down to PCBs on Asian made equipment and many of those will have seen what happens if the parts involved get hot.

The example on my bench is the SMPS from an Alesis powered monitor ( M1 Active, Chinese made) ) which has blown up big time because of the damn Yellow Glue used to secure a ferrite toroidal coil. All the glue used had gone brown or back ( ie carbonised ) on this coil and arced across nearby tracks taking out the main switching MOSFET, its drive IC and associated transistors, high speed diodes and even the AC bridge rectifier diodes.

The toroidal coil had to be un-wound, cleaned up and re-wound. The same glue was attacking parts elsewhere on the board too ( it corrodes copper) and had to be laboriously scraped off.

Are the dickheads who squirt this horrible goop all over PCBs NEVER going to wake up ??

..... Phil

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

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS
Reply to
Jeff Liebermann

"Jeff Liebermann"

** So you do no repair work at all ?

.... Phil

Reply to
Phil Allison

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

--
"Everything from Crackers to Coffins"
Reply to
Jeffrey Angus

"Jeffrey Angus"

** I've always wanted to know just WFT it really is !!

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

Reply to
Phil Allison

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.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS
Reply to
Jeff Liebermann

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

--
"Everything from Crackers to Coffins"
Reply to
Jeffrey Angus

"Jeff Liebermann"

** You are not a repair tech, or you would have seen it many times.

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

Reply to
Phil Allison

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.

Reply to
Gareth Magennis

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?

Reply to
N_Cook

that stuff is pure shit.

Reply to
Cydrome Leader

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

Reply to
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.

Reply to
Gareth Magennis

"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. ;-)

--
Jim Yanik
jyanik
at
localnet
dot com
Reply to
Jim Yanik

**No. It is a type of contact adhesive. It is still in widespread use, for reasons I don't understand. Some, more enlightened manufacturers, use a silicon type glue, which has a much higher burning temperature. 
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

going

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

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Reply to
Andrew Rossmann

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..

--
Live Fast Die Young, Leave A Pretty Corpse
Reply to
Meat Plow

"Alien"

** Correct.

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

No chance for moisture ingress there.

.... Phil

Reply to
Phil Allison

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

30 years breaks down to an oil, either itself corrosive or hygroscopic and then corrosive
Reply to
N_Cook

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

500 hours at 100C. Unfortunately, the resistance just keeps dropping after that.
Reply to
dewar

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