Cydrome Leader wrote in message
...
N_Cook wrote:
Here is a pic.
http://www.diverse.4mg.com/duff_cap.jpg
The leftmost is the bad cap, centre an older but unused Philips also
2.2uF
250V, and the third is from the same batch as the bad, not ohmic up to
30Mohm anyway

The 2 red s are "frames" 10&11 that show the curving and the graph
paper
behind where all the "silvering" is absent, so film colours consist of
silver, grey colour , hazy white and clear .
Centre is good "silver" and crystal clear polyester , only colours, with
alternate gutters for the edge connection, metal lead masses retained so
ragged edges from my unwinding.
Right one shows the same effect on the outer 4 frames but beyond that
the
metal foil is entire, but going home as the other.
Yellow case is the bad TC make and blue is 3 sides of the Philips puter
case. The philips actual capacitor volume is much less than the TC so
epoxy
filling , inside the block casing is complete, but both the others you
can
see the active film in a number of places , after removing the block
plastic
casing. This epoxy? inner encapsulation was much easier to break away
than
the Philips. I suspect the Philips used 100% epoxy and the TC had
fillered
epoxy so maybe making porous. No green corrossion products seen but I
assume
capillary migration of condensation through the poor epoxy from the open
end
with the leads or along the leads which were bright shiney in all of
them.
So this will be a generic fault with Electric Shepherd ESB55 , first
becoming apparent in the wettest county of Cumberland in 5 years of use
and
then other counties later presumably



I can't tell anything from the tiny photo, but a lack of metallization
sounds like the cap had the elctrodes burn from constant overvoltage or
breakdown/overload/ With such a low resistance, it may not be possible to
measure
the actual capacitance of the bad caps. It will drop as "self healing"
caps start to wear out. Something around 5% loss is considered end of life
for many applications.

Are you able to burn test the dielectric to see what it really is?




by burn test , this sort of discrimination?
http://www.boedeker.com/burntest.htm