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  • Capacitors!

    The audio on one of my Eumig S940s has been misbehaving a bit recently, with what can only be described as a 'crackle' underlying the sound which comes and goes. Sometimes you can have a night free of it, other times it's there, constantly.

    There's also been a bit of hum too. This is unusual because the Eumig S936/938/940 are far better in that regard than the 800 series Eumigs, where the hum seems to have been part of the original spec (!). I thought I would get round to adjusting the hum buck coils at some point to reduce it.

    Mindful of the fact that these machines are 40 years old now, I figured the capacitors on the audio board would be ready for replacement. Luckily I can get these swapped out at work and that's what I had done on Friday. There were about eight or ten of the bigger values that were replaced; only one of them had gone out of spec and not by much. The result was night and day however; the crackle has now completely disappeared, and to my great surprise, the hum vanished too. Bass was better and the whole sound experience was transformed.

    Steve Klare will be able to explain this sort of thing better than me, but capacitors are the one component on a circuit board that degrade over time, and they degrade faster if a machine is unused. This sort of thing can probably be done by an audio technician if you can't do this sort of thing yourself (I can't), and it's certainly worth having done. I'm going to have them replaced on all my projectors, whether there's a problem with the sound or not.

  • #2
    If changing your capacitors fixed crackling audio, My wild guess that the dielectric was actually starting to break down and what you were hearing was basically tiny lightning bolts within the caps themselves.

    -Nice work! (It could get nasty if they actually shorted out.)

    Years ago at one of my jobs I went to a presentation on how many different types of capacitors start to deteriorate within just a couple of years and should be replaced (...bearing in mind they were selling capacitors...just saying!). I've always been amazed to hear that at work and then come home and power up a projector with caps that were installed when I was in Junior High!

    This is a recent victim from my job:

    Click image for larger version  Name:	Blasto.jpg Views:	0 Size:	256.3 KB ID:	56135

    Tantalum Electrolytic Capacitor: 10 years old, -Rest in Peace!

    (I love troubleshooting like this: pop the cover, observe the blast damage, go see if the coffee is still hot!)
    Last edited by Steve Klare; March 13, 2022, 12:19 PM.

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    • #3
      Thankfully, I can’t imagine there will be too many Super 8 protectors with surface mount components, Steve. It would be a nightmare replacing those caps if they were tiny little things as in your pic!

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      • #4
        I agree totally with replacing capacitors in old electronic gear. I worked for many years as an IBM Field Engineer and also as a hobby, restored old radios. Some techs, when working on shortwave...and other vintage gear, just as a matter of practice, will replace all the caps before they do anything else. This is probably a good thing as 40-60 years of no use can mean that even if you replace a bad capacitor, the odds that another one will fail soon are high. Depending on where in a circuit a failing capacitor is, and how it fails...short, open, intermittent, etc. it can damage other critical and hard to obtain components. In any case, IF you buy an old tube unit of any kind, it's always good practice to turn it on the first time when it is hooked up to a variable voltage transformer. Old capacitors can often times be saved by "reforming" them...that means running them with reduced power for a few hours, then increasing the power until you reach full line voltage. Again, the BEST practice is replacing them all...especially the larger 'Electrolytic" ones...those oftentimes are the size of a small juice can...since the old ones were manufactured by rolling aluminum foil between waxed paper, they are the most likely ones to have gone bad. "Generally"..the small 'mica' ones (size of a postage stamp) will be OK...fingers crossed here...!

        Now...a few cautions and some safety advice. Remember that since there are NO "Radio Shacks" left and very few Radio-TV repair shops either, finding the correct parts for vintage gear can be difficult, as can deciding...and decoding, the values of capacitors, resistors, etc. in vintage gear. There are a few 'on-line' suppliers that generally have parts...a "Google" search can be your friend. IF you have no background or experience in working with older electronic equipment, this would not be something that I would recommend. Your best bet for any sort of DIY, would be to contact a Ham Radio Operator, as they usually have the knowledge and skills (and age!!) to help you along. Skills??..yep, replacing capacitors, etc. will require soldering...not a difficult thing to do, but having an 'Old Hand' to guide you would be invaluable as this is something that needs to be done correctly....!!! Remember too, that working on any of this gear means that it needs to be unplugged....and be aware that capacitors have the "capacity"...duh....to hold a voltage for sometime...and can retain that long enough and with enough voltage to give you a nasty shock. Just sayin'.....

        Steve, John and others....during my years of electronic work, we always said that the components in electric gear had a bit of smoke sealed in each one and it was that sealed smoke that contained the 'active stuff', that allowed the circuit to work. AND....whenever you observed that smoke escaping....(!!!!)..you could be fairly certain that the device had reached non-working status....!! We always got a BIG laugh out of saying that.....hope you do too...!

        John....great to read that your machine has been restored to correct operating condition....now maybe the only popping and crackling you hear will be coming from the popcorn....!![G]

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        • #5
          Yes,

          When I popped the lid on that one, I had a decent Idea what I was looking for. The tech that replaced this power supply said when he opened the rack door he "smelled capacitor"!

          -another unit of the same type failed a few days later...without the smell. THAT took some thought to fix!

          Parts-wise, I go to internet vendors like Digi-Key or Newark (-and others). One thing that Radio Shack was great for that short of a drone these other guys can't fix: when you are all done with the parts they delivered and you realize there is just one more that you overlooked, and if you had it you could finish in like 10 minutes!

          -Three days later plus delivery charges....

          Something you often run into replacing capacitors is what's available is different from years ago. For example axial cases are much rarer (the ones with a lead poking out each end), so you might be stuck using a radial (two leads same end) and get creative mounting and connecting it up. Something that can work to your advantage is capacitors of the same capacitance are smaller than they once were. When I got my Eumig 800 series, the hum bothered me. I jumped to the natural conclusion: "It's GOT to be the power supply cap in the amplifier!". I found that caps of the same value were now in smaller cases, but a cap of the same shape and size now had more capacitance. -So I replaced it with the larger value expecting lower hum than ever. If it did help, it sure didn't help a lot! -but that's a story for another day...(BTW, people on here that had been down this road warned me this would happen!)

          (Bearing in mind that if the value of the cap is critical, you may need to improvise mounting the smaller part.)

          What's bad lately is availability of parts. Last week I bought some fuses: silly regular-old glass cartridge fuses! -and earliest delivery I could get for them was July! There's a lot of that going on these days. (I subbed 15A for 16 to get them sooner...may fortune favor the foolish!)
          Last edited by Steve Klare; March 13, 2022, 04:12 PM.

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          • #6
            My much loved Yamaha EL90 orchestra stopped working a few years ago, a 9K instrument due to leaking cheap shrink wrapped caps. Upon opening it was a mess and although played every week those cheap components killed it. Its become common now with the EL range and best avoided which is a shame as it was a wonderful instrument to play.
            Replaced with another Hammond.


            EL90T
            Click image for larger version

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            • #7
              Hi Lee,

              There are a lot of ways for an electrolytic to die. Yes, you sidestepped the issue of being without voltage long term , but time and stress got them. (Eventually it gets us all!)

              It's kind of interesting how the time and stress work together. The more stress, the less time. The less stress the more time. Let's imagine you are a capacitor company and so am I. I manufacturer literally the exact same electrolytic caps as you do (I stole your designs: sorry!). Your 100V cap can really sustain 200V, but you rate it low for long life. I take your 100V part and rate it at 200V: full throttle! Your 200V part is actually good for 350V, so "my" 200V part is smaller and (-especially given my shoddy manufacturing and quality processes and pirate engineering) dramatically cheaper.

              -nonsense like this is why modern consumer electronics dies so young. Somebody building industrial or military or research quality electronics will buy their capacitors from you, but the guys looking to ship a million flat screen TVs that are meant for the landfill well within 5 years will buy "my" capacitors by the ton!

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              • #8
                I replaced the bigger value caps in both my Bauer projectors and it wasnt that difficult. Just needed care not to cause short circuits with sloppy soldering,and of course,getting the polarity correct.

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                • #9
                  I've discovered bad capacitors in two of my projectors so far. slowly replacing them all. Do one by one, and make sure to get the polarity correct. one leaked and almost ruined the board. fortunately caught before the damage was really bad.

                  The biggest enemy of electrolytic capacitors is the electrolyte drying out. Heat is the next big enemy, as it accelerates the process. heat can come from storage in an attic, from too much current through the capacitor, and from poor placement in the equipment. heat effects the electrolyte, but also the rubber seals that keep it in.

                  Always replace with roughly the same capacitance, never with lower voltage rating. If you're an engineer, maybe you can redesign the circuit better than the engineers who did design it... If you want the machine to work for a long time, buy only nichicon/panasonic/chemicon/rubycon. forget the rest for the most part. buy from a real parts house that can guarantee they're not selling you cheap knockoffs. never buy electronics parts like this from ebay or amazon. unless there is a pressing reason not to, I buy with the highest temperature rating, with the longest rated life, and the largest size physical size that will fit in circuit. when working with a printed circuit board, I try to always get replacements that have the same lead spacing so the the capacitor can sit all the way down snug on the board. stress from flopping around (especially with larger capacitors) can cause the leads to break off, and could cause more likelihood of corrosive electrolyte leaking out.

                  Electrolytic capacitor life is shortened to some extent with no use, but in use, they also lose life slowly but surely. Life ratings are shortened by excess temperature, so the cooler it runs, the longer it will last. life rating of 2000hrs at 85C seems low, but for the most part one doesn't run capacitors at such high temperatures if the equipment is designed well. for every 10C lower temperature or so, the life doubles. so with the capacitor at 45C instead of 85C, we're up to 32,000 hours of constant use. 3.65 years operating 24/7. 10000 hour capacitor rated at 105C is even better, especially if it is physically larger and dissipates heat better than a small one.

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                  • #10
                    the crackle may be the volume or tone control. spraying some electronic cleaner in there that is safe for plastic parts may solve the problem. isopropyl alcohol is good and sometimes comes in a spray can. I like CAIG fader lube to help keep the crackle from returning. may be some other intermittent connection, or a bad solder joint somewhere.

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                    • #11
                      Originally posted by Jon Byler View Post
                      the crackle may be the volume or tone control.
                      No, it was definitely the caps having gone out of spec - there's no noise at all now. It was there all the time. With noisy pots, they tend only to be noisy when operating them.

                      The Eumigs I have (and the Bauers) have sliding volume controls that don't respond well to cleaning, even with fader lube. It seems to strip out their original lube making them more difficult to use so I don't tend to use it on them.

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                      • #12
                        With capacitors, it's definitely true that you get what you pay for and that cheap ones will not serve you well.

                        The good news for 8mm enthusiasts is that most of the equipment will not be working at higher voltages, making replacement capacitors easy to find.

                        I would suggest RS ( https://www.rs-online.com/ ), DigiKey ( https://www.digikey.com/ ), or Mouser ( https://www.mouser.com/ ) as good places to start.

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