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Thread: Apple /// line filter go boom

  1. #1
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    Default Apple /// line filter go boom

    Had my Apple /// up trying to figure out why ADTPro no longer comes up on my Win 10 box... and I hear this low 'thuwh' noise.. and then I heard light crackling, like the sound sparklers make. And then smoke. Lots of smoke. Smoke for about 15 minutes after I killed the power.

    Since the computer kept running even as it initially smoked, I knew it was most likely the line filter thingy, and sure enough when I opened it up, I can see the 0.22uf filter has blown open. Not nearly as dramatically as the one on the PSU for my Commodore PC-II, but same idea.

    I've never replaced one of these things.. are they pretty standard? Just one of these: https://www.ebay.com/itm/10pcs-0-22-...frcectupt=true ?

    Is there anything else in the PSU I need to worry about after this?

    I gotta get out of here. This room stinks to high heaven!

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    Well since you are in the PSU a full recap would not hurt for preventative maintenance.
    = Excellent space heater

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    I suspect the cap that went fizzle-bang was a Rifa fim cap. They age badly and do fail. Clean up and replace it. If the system runs, I wouldn't bother with the other caps until it starts acting up.

    It's strange--those Rifa caps are highly prized by the audiophile crowd.

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    Quote Originally Posted by Chuck(G) View Post
    I suspect the cap that went fizzle-bang was a Rifa fim cap. They age badly and do fail. Clean up and replace it. If the system runs, I wouldn't bother with the other caps until it starts acting up.

    It's strange--those Rifa caps are highly prized by the audiophile crowd.
    I really rather doubt that this particular style of RIFA capacitor would be prized by anybody for sound quality, since they're rarely, if ever, used with an audio signal across them. There are two types of these so-called "safety capacitors", X-class and Y-class. The X-class capacitors are meant to be installed across the power line, while Y-class capacitors are intended to be installed from one side of the line to ground. I've also seen safety capacitors which contain both; such caps, naturally, have three leads on the bottom instead of two.

    And yes, they're quite notorious for their smoke output. Had one go in my Macintosh 512K, and it damn near fogged up the basement. Only more dramatic case I've seen was while testing an old Zenith "TransOceanic" tube 'portable' radio, where a 0.47F@600V molded-paper "bumblebee" capacitor across the power line decided to go bang. Saw a nice bright flash from under the chassis, followed by a big plume of smoke out the top of the case with the radio still playing like gangbusters. When I pulled the chassis, the striped middle section of the capacitor rolled out onto the floor, having been perfectly blown clear of its lead-ends.
    -Adam

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    The computer itself seemed to be fine.. it kept running even as smoke poured out the back. I've confirmed that is what it was... it's a yellow square, markings on it are 0.22uf, x2, 250v. Bottom corner of it is blown open. Didn't go as spectacularly as the one on my PC II... but definitely is blown. I'm assuming same rules apply as with other caps... just make sure uf is correct and voltage is not lower? I'm wondering if physical size is something I have to watch out for... they don't post that on ebay or other electronics sites.

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    Quote Originally Posted by AdamAnt316 View Post
    I really rather doubt that this particular style of RIFA capacitor would be prized by anybody for sound quality, since they're rarely, if ever, used with an audio signal across them. There are two types of these so-called "safety capacitors", X-class and Y-class. The X-class capacitors are meant to be installed across the power line, while Y-class capacitors are intended to be installed from one side of the line to ground. I've also seen safety capacitors which contain both; such caps, naturally, have three leads on the bottom instead of two.

    And yes, they're quite notorious for their smoke output. Had one go in my Macintosh 512K, and it damn near fogged up the basement. Only more dramatic case I've seen was while testing an old Zenith "TransOceanic" tube 'portable' radio, where a 0.47F@600V molded-paper "bumblebee" capacitor across the power line decided to go bang. Saw a nice bright flash from under the chassis, followed by a big plume of smoke out the top of the case with the radio still playing like gangbusters. When I pulled the chassis, the striped middle section of the capacitor rolled out onto the floor, having been perfectly blown clear of its lead-ends.
    -Adam
    Not Rifa safety caps per se, but the Rifa film capacitors in general (of which the safety caps are a subset). I've got a pile of the non-safety ones.

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    Quote Originally Posted by falter View Post
    The computer itself seemed to be fine.. it kept running even as smoke poured out the back. I've confirmed that is what it was... it's a yellow square, markings on it are 0.22uf, x2, 250v. Bottom corner of it is blown open. Didn't go as spectacularly as the one on my PC II... but definitely is blown. I'm assuming same rules apply as with other caps... just make sure uf is correct and voltage is not lower? I'm wondering if physical size is something I have to watch out for... they don't post that on ebay or other electronics sites.
    That's typical for line filter capacitor explosions. As I noted above, the tube radio I was testing continued to play just fine after its line bypass capacitor blew itself apart. As far as a replacement, I'm not sure if the exact value is especially important, as long as its close, and that the AC voltage rating and safety class are similar or identical. I need to order a bunch of safety caps myself; I was hoping to find them at one of my local electronics supply shops (there actually are a few in my area), but it's not the sort of thing which NTE offers, for some odd reason.

    Quote Originally Posted by Chuck(G) View Post
    Not Rifa safety caps per se, but the Rifa film capacitors in general (of which the safety caps are a subset). I've got a pile of the non-safety ones.
    As far as I know, the innards of RIFA film capacitors are just as good as other film caps. The way I understand it, the main culprit in what makes their line safety capacitors so incendiary in nature is that amber resin coating they used. It shrinks over time, cracking around the innards (which apparently used old-style paper dielectric, for some odd reason, rather than more modern film), and letting moisture in. Once enough moisture has been absorbed, it's only a matter of time before a voltage spike comes along the power line, and kablammo.
    -Adam

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    Quote Originally Posted by AdamAnt316 View Post
    That's typical for line filter capacitor explosions. As I noted above, the tube radio I was testing continued to play just fine after its line bypass capacitor blew itself apart. As far as a replacement, I'm not sure if the exact value is especially important, as long as its close, and that the AC voltage rating and safety class are similar or identical. I need to order a bunch of safety caps myself; I was hoping to find them at one of my local electronics supply shops (there actually are a few in my area), but it's not the sort of thing which NTE offers, for some odd reason.
    What denotes the safety class? Is that the 'X2' marking?

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    Quote Originally Posted by AdamAnt316 View Post
    As far as I know, the innards of RIFA film capacitors are just as good as other film caps. The way I understand it, the main culprit in what makes their line safety capacitors so incendiary in nature is that amber resin coating they used. It shrinks over time, cracking around the innards (which apparently used old-style paper dielectric, for some odd reason, rather than more modern film), and letting moisture in. Once enough moisture has been absorbed, it's only a matter of time before a voltage spike comes along the power line, and kablammo.
    That's been the common understanding. Add to that, a filter cap across the AC line does experience more self-heating than a simple capacitor used for audio signal coupling. At any rate, I've got a bucket of the Rifas, from 2 uF on down into the pF range.

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    Quote Originally Posted by falter View Post
    What denotes the safety class? Is that the 'X2' marking?
    Correct. 'X' denotes a capacitor intended to be installed across the power line, while 'Y' denotes one meant to be connected between one side of the power line and ground. Any of the X-code safety capacitors would work just fine in this application; a Y1/Y2 capacitor would be acceptable in X1/X2 duty, but not vice-versa. An article on the subject of X/Y-rated line filter capacitors can be found here.

    Quote Originally Posted by Chuck(G) View Post
    That's been the common understanding. Add to that, a filter cap across the AC line does experience more self-heating than a simple capacitor used for audio signal coupling. At any rate, I've got a bucket of the Rifas, from 2 uF on down into the pF range.
    Generally, so-called "safety" capacitors are designed to not fail in the manner in which these Rifas do. Sure, they're probably meant to either go open or short, but they're definitely not supposed to blow up or potentially cause a fire. I'm pretty sure that more modern Rifa capacitors aren't prone to this issue, at least as long as they've stopped using that cursed resin.
    -Adam

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