Substituting Polyester Film Capactitors (Sound System) - Page 1
Forum section: electronics / repair

author: Traceless
author_rank: Frequent Contributor
timestamp: August 17, 2025, 01:24:38 pm
content: Hi everyone,I need to replace some polyester film caps (100V types, e.g. 2A104J, 2A334J, 2A473J ...) on an audio amplifier board. Looks like the "reputable" shops don't offer those anymore. Is there any good, leaded modern substitute with similar-ish lead spacing I could drop in? Plan B would be to get a pack in the Aliexpress capacitor lottery.The original caps look like these ones:

author: jfiresto
author_rank: Frequent Contributor
timestamp: August 17, 2025, 02:50:11 pm
content: Will WIHA MKS-2 not work, for examplefrom Reichelt? Or has Reichelt become disreputable?

author: Traceless
author_rank: Frequent Contributor
timestamp: August 17, 2025, 05:24:07 pm
content: Quote from: jfiresto on August 17, 2025, 02:50:11 pmHi jfiresto, tbh I was looking at DigiKey and Mouser and found they didn't offer any of the old-school Polyester film caps. If the WIMAs work as a substitute, they will absolutely suffice. The thing is I know that certain types of capacitors have certain characteristics that make them more or less suitable in certain applications. However I don't know a whole lot about those older-style polyester film caps, their particular properties and how they compare to newer style film caps, particularly when used in audio equipment. I could probably also drop in leaded ceramic caps (e.g.this one) - the question is would that be a good idea. So based on your answer I assume the WIMA ones will do the job.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 17, 2025, 06:05:52 pm
content: Polyester caps are cheap, not special. Well, they are a film type, so better than ceramic X7R!You did not post the (by far) most important piece of information--what are you repairing? "Audio amplifier"? Not helpful!Unless you are repairing something exotic any cheap film cap (non-ceramic!) will do. Wima MKS2 fits the bill.

author: TimFox
author_rank: Super Contributor
timestamp: August 17, 2025, 06:18:58 pm
content: Searching Mouser for capacitors & film & radial termination & polyester pulls up many parts in two styles:Boxy, with two short leads, not mechanically suitable for you,OrLeaded parts from Panasonic (ECQ series) or Vishay/BC (BFC series) in different voltage ratings.

author: Traceless
author_rank: Frequent Contributor
timestamp: August 17, 2025, 07:07:56 pm
content: @RandalMcRee: I'm not repairing anything fancy just an old-ish Logitech Z3 Sound system. It did sound quite well also the build quality was way better in that one compared to the newer ones. The satellite speakers had real metal stands and are well made. New ones are cheap plastic only. The board is very similar to this one of a slightly later model (Z340), The Chip in the back is a TDA7377:Someone also made a teardown video of an actual Z3here.@TimFox: Thank you for pointing out the different form factors the WIMA ones indeed seem a bit wide.

author: Seekonk
author_rank: Super Contributor
timestamp: August 18, 2025, 12:09:28 pm
content: Hard to imagine caps like that would ever need replacing.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 18, 2025, 01:25:43 pm
content: From my experience these green caps never need replacing unless mechanically damaged. Why on earth would you want to replace them?!CheersAlex

author: wraper
author_rank: Unknown
timestamp: August 18, 2025, 01:40:31 pm
content: Replace them for what? For not having anything better to do than wasting your time and money on a useless endeavor? These capacitors fail only under severe stress, such as when run under high voltage, high temperature and high ripple current (like in incandescent bulb ballasts), which you'll never see in an audio amplifier like this.

author: Traceless
author_rank: Frequent Contributor
timestamp: August 18, 2025, 07:01:10 pm
content: @Seekonk,@Alex Nikitin,@wraper: An electrician made a mistake and cut the mains neutral, needless to say that s**t hit the fan big time (aka.Sternpunktverschiebungin German, sorry I don't know the correct english term and the dictionary doesn't help either. Maybe you can autotranslate the wikipedia entry with the browser). Unfortunately among other stuff those speakers were hooked up when that happened. Now I get 230 VAC leaking through on the 3.5 mm headphone jack. Normally I'd suspect X/Y caps leaking from the primary to the secondariy side but this one has a linear supply. So the only reason I can imagine is either some of the caps leaking or something wrong with the transformer. If its the latter its probably game over anyways so I thought I'd give it a shot and see if swapping the caps helps.

author: wraper
author_rank: Unknown
timestamp: August 18, 2025, 07:31:47 pm
content: Quote from: Traceless on August 18, 2025, 07:01:10 pmIt's beyond ridiculous to think that replacing capacitors on the amplifier board will help with mains voltage leakage. Hello, this board is supposed to be isolated from the mains voltage to begin with. How did you test the voltage leakage? If it's transformer issue, you should be measuring resistance between primary and secondary windings, not replacing capacitors on the amplifier PCBQuoteRegular transformer does not mean there is no capacitance at all between its windings.

author: Traceless
author_rank: Frequent Contributor
timestamp: August 18, 2025, 07:44:44 pm
content: Quote from: wraper on August 18, 2025, 07:31:47 pmUnfortunately with my first with my fingers, because I was reconnecting cables and didn't expect any surprise AC on audio cables. It seems there is enough current to give you that prickly/tingly/stingy sensation but not enough to trip the RCD when you touch PE with the cable (so maybe a few mA)?. Anyways after surprise voltage I used the DMM to measure between 3.5mm Jack and PE on a socket.Quote from: wraper on August 18, 2025, 07:31:47 pmThe funny part is the thing still turns on and there is no visible damage on the inside. It doesn't trip the breakers so a full short between transformer primary and secondary is also out of the question. TBH I'm currently not quite sure what is going on.

author: madires
author_rank: Super Contributor
timestamp: August 18, 2025, 08:28:09 pm
content: Do you have that voltage between the audio jack and PE when nothing is connected to the sound system (besides the power supply and the DMM)?

author: wraper
author_rank: Unknown
timestamp: August 18, 2025, 08:29:23 pm
content: Quote from: Traceless on August 18, 2025, 07:44:44 pmThis assumption is a total nonsense as well. Circuit breaker has nothing to do with tripping on failed insulation and has no way to detect it. Not to say it the speaker is earthed, or something else was connected to it, it might be that you being hit does not even have anything to do with the speaker itself and you are butchering it for no good reason.