Old school green resin film capacitors? - Page 1
Forum section: electronics / repair

author: HooRide
author_rank: Regular Contributor
timestamp: November 21, 2022, 04:51:26 am
content: Hello All, I'm repairing the power supply of a decade old powered subwoofer for a friend. After 20+ years of fixing things I've finally found a bad film capacitor; I usually don't even bother testing them.Since this is my first time replacing one, I only now realized I can't find any similar looking parts on Mouser or Digikey.I've got a 104J / 100V like the picture attached.Is this some style that just isn't made anymore? Do I replace with readily available epoxy-filled rectangle packages?Thanks!

author: tautech
author_rank: Super Contributor
timestamp: November 21, 2022, 05:07:05 am
content: This should help you select a suitable replacement from modern types:https://exxelia.com/uploads/PDF/5a9d67159adff.pdf

author: HooRide
author_rank: Regular Contributor
timestamp: November 21, 2022, 05:12:58 am
content: Oh, if I can replace with ceramic, that's even easier. Many thanks!

author: John B
author_rank: Frequent Contributor
timestamp: November 21, 2022, 06:09:43 am
content: Err, what. Don't change it for a ceramic type, it's a polyester cap for a reason, eg in the audio path.I didn't have any trouble finding those greencaps the last time I looked, but it's not as though you're limited to them. A polyester or polypropylene cap in a more modern box shape will be fine if the lead spacing is close enough.edit: although it's specified as being in the power section, there's going to be some reason for it. Perhaps the voltage rating.

author: srb1954
author_rank: Super Contributor
timestamp: November 21, 2022, 06:11:51 am
content: Quote from: HooRide on November 21, 2022, 05:12:58 amWithout knowing its circuit function I would stick with the original polyester (PET) style cap rather than substituting a ceramic cap. Ceramic caps, unless you are using expensive C0G types, have greater variation in capacitance value versus applied voltage and temperature compared to polyester caps. This variation may affect the performance of your circuit, particularly if subject to higher temperatures. Judging by the darkening of the green colour of your faulty sample I would say it has been subject to some fairly high temperatures for a prolonged period.Polyester caps are still readily available from the usual distributors although more usually in a stacked film design rather than the wound film design of your example.

author: Whales
author_rank: Super Contributor
timestamp: November 21, 2022, 06:22:42 am
content: +1 to not replace with any old ceramic because you say it's in a subwoofer circuit. It might be perfectly fine (low voltage swing) or it might introduce notable distortion (lots of voltage swing).104J (100nF) is probably available in more linear ceramic chemistries if you know what to look out for. At this capacitance level you will find most items sold are the nonlinear ceramic chemistries.Most film capacitor variants have very good performance, I would not worry about which particular polymer type is used unless it's a particularly high voltage or high current circuit (in which case the cap would look a lot bigger than what you picture).Digikey does have quite an expansive selection of film caps, including 100nF (0.1uF) 100V+ rated items. Most of them are cast in little rectangular plastic boxes rather than just being resin dipped, so they look a little different to the curvy lollies you are used to. Most of them will also be rated to much higher voltages (their main market will be 120/240V mains) but I don't believe it would cause you any issues.LCSC also stocks lots of film caps, including the dipped curvy lolly style you photographed. They are cheaper per unit than digikey, but of course shipping might not suit you. Oddly they split things into two categories:https://lcsc.com/products/Polypropylene-Film-Capacitors-CBB_554.htmlhttps://lcsc.com/products/Film-Capacitors_982.html

author: Berni
author_rank: Super Contributor
timestamp: November 21, 2022, 06:24:45 am
content: Don't just replace it with ceramic without knowing what it is for. Ceramics can distort signals.What you need to look for is any film type capacitor. The kind of dielectric inside doesn't really matter, they all perform well for signal processing. Some of the modern ones might look like rectangular plastic boxes but the look doesn't matter. There are also film capacitors in SMD form, but those need careful handling during soldering.

author: John B
author_rank: Frequent Contributor
timestamp: November 21, 2022, 06:31:17 am
content: SMD ones are usually expensive compared to through hole ones too.