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Thread: How do you know when it is time to recap?

  1. #1
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    Question How do you know when it is time to recap?

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    Why would one recap a piece of gear? How do you know it is time? I've seen pics of what bad caps look like, and I don't think I've seen any in my gear that I've had open, but I saw a post by an M320 owner who had recapped their mixer, and I'm thinking about my M520 which is of similar vintage and I'm wondering if it is something will need to do eventually, or if it is something that it needs now and I haven't identified that yet...

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    If your mixer works well, don't bother recaping right now if you don't have test equipment.
    To see if a capacitor needs to be changed, you have two tests to do:
    1) Capacitance
    2) ESR (Equivalent Series Resistor)

    The first one is trivial to test with multitesters. The latter needs a special tester like the Capacitor Wizard (search Google). While the Capacitance requires removing the cap (at least one leg), the ESR can always be tested without disconnecting anything.

    Any capacitor with a weak ESR needs to be replaced. Those with drifted capacitance require attention: if the capacitance is still in the original tolerance and that the ESR is ok, then the capacitor is good. Else, you need to chance it.

    There is also a quite large tolerance of capacitance drift. Electrolytics which reduce by 10% and even 20% will generally work well.
    The two common troubles with them are either when they are dry (no sound or a lot of distorsion) or get shorted (same with possible damage in specific sections).
    Personally I consider recaping a reel recorder when it's 25+ years old. I also got familiar with sertain types of capacitors which are always bad or weak, and which I always change.
    With a power amplifier, any noticeable "hiss" ("souffle" as we say in french) in the speakers means that at least the electrolytics in the rectifier section, and/or those before the speakers, need to be replaced.
    With reel recorders, it depends whay section is affected by bad capacitors.
    In a mixer, I have no knowledge, but would consider recaping only one section and compare the sound with an untouched one by sending the same mono signal to both inputs.
    In any case, electrolytics can produce real troubles, especially those from the late 1980s or 1990s which are even worse than the good old ones. I've seen so many VCRs from that era which had leaky caps, whereas my old JVCs HR-3300 from 1978 and HR-7600 from 1983 still work great with their old caps.


    David.

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    ESR-meter diy project here: http://www.ludens.cl/Electron/esr/esr.html, it's a relatively easy to build one. I have a short eMail chat with the man behind it - a nice guy, dedicated to the 'big "hobby" '
    I've built one, following Manfred's design (details here: http://www.mzentertainment.com/studi...esr_meter.html ). It works great from my experience. A nice tool to have around.
    **************
    "How do you know when it is time to recap?"
    I would say - when it's bad - replace it.
    *********
    Preventive recaping may make perfect sense for some, I guess. I would not argue with that, as long as it makes a "doctor" happy and keeps him busy
    If you do a lot of repair work, you get better "sense" about what and when and what is more likely to go bad from experience, just as David said: "I also got familiar with certain types of capacitors which are always bad or weak, and which I always change."
    Knowledge is calculable, Ignorance has no limits.
    Dr ZEE
    MZE | Dr ZEE WORKSHOP

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    mid -low end gear use mid-low end parts... duh??? so if we're talking bout this kinda gear then any electrolytic that's in the 15 yr range is suspect... especialy if it has gone sometime without being used... yes lack of use can be VERY bad for electrolytics... do you find that adjacent channels dont sound reasonably alike???? that's a cap problem... have you cleaned the controlls but still find it's scratchy sounding??? often that's coupling caps...
    37.8% of all statistics are made up on the spot...

    hey give a guy some room... people are trying to evolve here... for crying out loud...

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    Quote Originally Posted by dementedchord View Post
    ... if we're talking bout this kinda gear then any electrolytic that's in the 15 yr range is suspect...
    from wikibicyclopedia :
    "The presumption of innocence being innocent until proven guilty is a legal right that the accused in criminal trials has in many modern nations. The burden of proof is thus on the prosecution, which has to collect and present enough compelling evidence to convince the judge and jury, who are restrained and ordered by law to consider only actual evidence and testimony that is legally admissible, and in most cases lawfully obtained, that the accused is guilty beyond a reasonable doubt."
    Knowledge is calculable, Ignorance has no limits.
    Dr ZEE
    MZE | Dr ZEE WORKSHOP

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    Quote Originally Posted by Dr ZEE View Post
    from wikibicyclopedia :
    ok... so you're saying that the caps have the right to interfere with the accurate transmission of audio up until the point that any plebe would deem them bad??? no points given for a knowledgeable and/or experienced prosecutor/tech?? or can they only be prosecuted by one having benefit of oscilloscope and knowledge there of???
    37.8% of all statistics are made up on the spot...

    hey give a guy some room... people are trying to evolve here... for crying out loud...

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    heh heh, that's a good one I'll do my best trying to follow
    Quote Originally Posted by dementedchord View Post
    ... you're saying that the caps have the right to interfere with the accurate transmission of audio...???
    Wikibicyclopedically speaking, - Yes.

    Quote Originally Posted by dementedchord View Post
    no points given for a knowledgeable and/or experienced prosecutor/tech??
    When the points are due - they shall be given.
    Justice!

    Quote Originally Posted by dementedchord View Post
    or can they only be prosecuted by one having benefit of oscilloscope and knowledge there of???
    I don't know. Never tried using oscilloscope nor knowledge thereof to specifically determine the guilt of a cap. But then again, there are many things I've never done. So, I don't know.

    One thing I know for sure, however, that recaping does not really require any knowledge. It only requires an ability to take a cap out and place a cap in. It's a popular thing to do, and fun too

    /respects
    Knowledge is calculable, Ignorance has no limits.
    Dr ZEE
    MZE | Dr ZEE WORKSHOP

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    Hey Mike, I get your point...I think my concern is of the cap with the willful intent to inflict harm, or rather I guess incapacity (no pun intended) to refrain from inflicting harm.

    If a cap going bad can take out other components, I want to avoid that. I'm not into "guilty before being proven innocent", or doing needless work, but if the cap has the built in inability to not inflict harm on others as it dies, then it needs to be taken out...like one of these...
    Attached Thumbnails Attached Thumbnails roy-jpg  

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    Quote Originally Posted by sweetbeats View Post
    the cap has the built in inability to not inflict harm on others as it dies...
    I dig that line ,
    Would not it be great if there was such thing as a free of 'inability to not inflict harm' cap? .
    Have you Ever wondered about the reasons behind the fact that insurance businesses eat us all alive and do so with a wide smile ?

    In all seriousness, - recap away! It will not hurt.
    Knowledge is calculable, Ignorance has no limits.
    Dr ZEE
    MZE | Dr ZEE WORKSHOP

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    if you can do general soldering than you should be able take care of the project in a couple hours, depending on the number of caps.

    Also you ONLY have to change electrolytic caps, dont replace all the small ceramic disc and others. unless you dig that sorta thing.

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