On 19/06/2015 09:04, Arfa Daily wrote:




Why would they have to be unpolarised? Just 2 paralleled together to
get the required capacitance. Any polarising mark on the SM carrier
strip perhaps


I don't think that they *do* have to be un-polarised, as such, given the
ones that Phil has found. I think it's just because they *are*, if you
see what I mean. To be honest, I never knew that you could get
multilayer ceramics in such high values. Presumably, they don't go up as
high as 47 uF which the designer felt he needed, so he just put 2 x 22
uF in parallel instead. As I said, the circuit is absolutely un-critical
in that it only needs to produce a small amount of DC from the incoming
mains to power the LED in the opto that produces the muting signal.
Because of time constraints with ordering-in those ceramics, I think I'm
just going to go with a pair of small tants, fitted to observe their
polarity.

Arfa

So to get that capacity in that package , they must be seriously multi
MLCC. Was it actually dead short or very low resistance. I suspect the
usual metal migration failure mode of MLCC , then paralling-up just
increases the chance of failure , for the circuit. Someone mentioned
paralling ten , asking for trouble.