Help Id Type of Capacitor

[Silveruser]

Can anyone help me id the type of these capacitors - the silver rectangle ones. I've spent some time looking at pictures and listings - nothing like them so far. They are through hole/leaded parts. Marked 470n and 220n on the schematic.

[Cyberdragon]

Why would they leave them bare like that?

[Silveruser]

Thanks blueskull, I guess flame proof coatings weren't important back then. This board dates from appox 1991 still works fine, but another one not so much.

[David Hess]

My guess is polyester film capacitors which is a little unusual for linear regulator decoupling.  Any film capacitor would work as a replacement.

[SeanB]

Naked polycarbonates, mostly made by Siemens and Phillips as a low cost non encapsulated capacitor. They were made by producing a very large circle of capacitors, spraying the end schoop coat on and then slicing the circle into small sections, and then welding on the end leads. Siemens did make a range with dipped ends, generally a blue coat.

[frantisek]

Very reliable. I have not found a bad piece yet!

[T3sl4co1l]

Don't know about those exactly, but similar modern caps (PPS dielectric, SMT chip package) do suffer from the layers trapping flux and therefore leakage, no matter how much you clean it.  Only relevant to low leakage applications, not aware of other issues.

Tim

[floobydust]

I believe those are Epcos SilverCap B32560 series, still sold today.
I have no idea why- they can be fragile if you bump them and I use boxed parts. I had lots in 1980's when Siemens or Epcos mylar/polyester MKT caps first came out.

edit: they're good parts and I've never seen one fail

[Silveruser]

Thanks for the info everyone. Looks like they came into use after I got bumped up to a more management role, not something I member seeing. Also sounds like they could be okay unlike the tantalums on earlier designs of the board. I don't have the bad one in hand yet so will have to see whats up when I get it or find someone closer to have a look.

George

[SeanB]

Yes they are great caps, only do not use on mains, do not use in an environment where the capacitor will be exposed to high voltage ( over 30V) in humid climes and do not use for any pulse application. They do burn off ends in pulse applications, and the top and bottom of the capacitor 9 along with the ends of course) are conductive, so leave a gap under the cap when soldering to a board, or the flux residue there will cause leakage.

They do make a nice orange spark when they arc over, and I have soldered wires onto the Schoop ends on occasion when the end wire broke loose from the spot weld. Very fast and pre tin the wire end with a blob of solder.