"Lund-Nielsen, Jorgen" wrote in
:

Am 07.09.2011 22:42, schrieb dewar:
On Aug 30, 8:59 pm, "Phil wrote:
** 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

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.


I'm thinking that outgassing electrolytes from the
Elytics also do a further degeneration of that glue.
Seen some discoloring and very low impedance in the goop around some
Elytics even in cases where the temp was not high...


Jorgen
dj0du





should electrolytic caps BE outgassing under normal operation?
I don't think so.
maybe it enhances the glue's degradation after the cap begins to
fail,making the problem worse,leading to charring of the PCB.

--
Jim Yanik
jyanik
at
localnet
dot com