Power line entry EMI common-mode filters - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 19, 2017, 11:33:18 pm
content: OK, I received my Tektronix vectorscope and waveform monitor, so I took it apart as part of my incoming inspection.I saw the twin horrors of Schaffner power line filters and RIFA caps in the power supply.Capacitors I can buy, but how in the @*^&%^*%! are these stupid filters worth 10-15$ on Digikey?I'll pay more to buy two of these stupid things than I paid for the vectorscope.I have a bunch of panel mount filters in my stash, but I want specifically the PCB mount version.Anyone have a part # with three leg PCB mount that's maybe 5$? It only needs to pass 1A.FN-326-1/02Or are these things really that expensive? If so, I'm taking the torch to mine and taking the potting out and putting in my own filter ...

author: james_s
author_rank: Super Contributor
timestamp: December 19, 2017, 11:36:07 pm
content: What's wrong with the filter? Why not just leave it alone?$15 doesn't really sound all that expensive to me, people's expectations have certainly been lowered by all the cheap gear from China. When I need one of those filters I usually salvage one from some discarded equipment.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: December 20, 2017, 01:02:34 am
content: If you can buy it for 15$ on Digikey, why design it?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 20, 2017, 01:16:54 am
content: Quote from: skipjackrc4 on December 20, 2017, 01:02:34 amPrecisely. To make one myself would cost thousands in NRE. Just try to imagine how they extrude that little housing? They stamp them out so fast it's just a blur coming out the other end.But, since this is 15$, not 4$, for basically a handful of passives in a metal housing, the search continues.

author: james_s
author_rank: Super Contributor
timestamp: December 20, 2017, 01:23:22 am
content: I'm still not sure why you need to replace the filter in the first place? I've never had one of those go bad. I'm not sure how much your time is worth but it must not be very much if it's worth an extended search to find something cheaper than a readily available $15 part.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 20, 2017, 01:23:53 am
content: Quote from: james_s on December 19, 2017, 11:36:07 pmYou've never heard of Schaffner and RIFA? Time bombs. Replace on sight.Quote from: james_s on December 19, 2017, 11:36:07 pmWell, it is the season of giving. You can mail me two in time for Christmas?Quote from: james_s on December 19, 2017, 11:36:07 pmOf course, I have a bunch, but I want specifically the three-pin PCB mount version.

author: james_s
author_rank: Super Contributor
timestamp: December 20, 2017, 01:25:52 am
content: Quote from: Alex Eisenhut on December 20, 2017, 01:23:53 amI've never heard of issues with them, I'm sure it happens but I must have a dozen or so in various pieces of equipment and none have ever given me any trouble. I'm not going to replace one unless it fails, at which point I don't think $15 is at all unreasonable.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 20, 2017, 01:34:23 am
content: Quote from: james_s on December 20, 2017, 01:23:22 amClearly, if I bought a vectorscope in 2017.... it's for hobby purposes? So time I have plenty, 15$ for a punched metal carcass with a handful of caps, not really. It's a useless piece of equipment that I bought for the price of a six pack of grocery store beer.I'm not buying two 15$ line filters for this...And really, you never heard of Schaffner line filters and how they like to catch fire? Seems the topic pops (haha!) up fairly regularly wherever they were used.Maybe they're better now, but in old test equipment, they blow up. I am specifically talking about Schaffner in vintage equipment.https://www.vintage-radio.net/forum/showthread.php?t=88137https://www.eevblog.com/forum/repair/hp3458a-schaffner-mains-line-filter-failure/So when I saw these little pieces of crap in my vectorscope, I was a little disappointed. Oh well, had to happen to me sooner or later.So yeah, I'm not waiting for them to fail, since it will cost far more than 15$ to repair that damage.I think I'll keep searching. Part of the thrill is finding a bargain.