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Microscope capacitor exploded

Discussion in 'Troubleshooting and Repair' started by Bruce Taylor, Feb 2, 2014.

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  1. Bruce Taylor

    Bruce Taylor

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    Feb 2, 2014
    Hi, I know nearly nothing about electronics, but occasionally manage to fix things. :) Maybe somebody here can help me with this.

    A few months ago, a capacitor in the base of my 70s-era Olympus microscope went off like a firecracker, spraying a confetti of cardboard and foil out of one end. When the foul-smelling smoke cleared, the microscope still worked, and I continued to use it for several months. However, shortly after we moved to a new area, it started burning out bulbs (which are very expensive!). I am guessing that the capacitor is supposed to play a role in grooming / smoothing the power, protecting the bulb...and perhaps the lamps dislike the power in my new area?

    Anyway, I'd like to fix it, if I can find the part I need. I have no schematics, but the capacitor's values are printed on the barrel:

    [​IMG]

    As I interpret this, it was a .1 uf capacitor, 500 volts DC. I am not sure what the {M} means (perhaps short for the manufacturer, Marcon?). And I have no idea what the 20k stands for. I believe the pins both emerged from the same end of the barrel.

    I've Googled around a bit, trying to find a source for a similar part, but haven't had much luck. It's an old part, and I am not sure what modern substitutes I can safely use to replace it. Also, I have no idea where I might go looking for such a thing.

    If anyone can point me to a suitable replacement, I'd be very appreciative.

    If it is of any use, here is a picture of the microscope base:

    [​IMG]
     
    Last edited: Feb 2, 2014
  2. duke37

    duke37

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    Jan 9, 2011
    The capacitor looks to be close to the input switch so may be a suppression capacitor across the mains. i do not know what the M means, if it were a resistor it would be a 20% tolerance.

    I suggest that you replace with a modern 600V or 1000V capacitor.
    The bulb failing may be due to a higher mains voltage. What does the potentiometer do?
     
  3. Bruce Taylor

    Bruce Taylor

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    Feb 2, 2014
    Thanks so much for the quick reply. I think the potentiometer is associated with the dimmer function (the slider at the bottom of the second image). That gauge on the left is a voltage indicator, which has not functioned while I've had this 'scope.

    OK, I'll see if a 600v or 1000V replacement is available. Is there a particular type of capacitor I need to get? For instance, does the shape of the capacitor matter? While Googling, earlier, I found that some vendors had rectangular or disk-shaped capacitors with similar values. I know it should not be a complicated repair, but I am not even sure whether this capacitor is electrolytic or non-electrolytic!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If it's connected to the mains, get an X rated capacitor. They are rated to be safely placed across the mains. There are other similar ratings X2, Y, etc., with more stringent requirements.

    You can read more about them here. (There are a plethora of explanations, this is just the one I found first today)

    edit: it's not electrolytic (one give-away is that it's not marked with a +ve and -ve lead).
    edit2: OK, so usually only 1 lead is marked with a polarity, often the negative
     
    Last edited: Feb 3, 2014
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Hi Bruce and welcome to Electronics Point.

    I'm not sure that the value is 0.1 µF. The marking that might be a decimal point looks more like a comma, and I don't think it's made in Europe where commas are used as decimal points - Marcon seems to be a brand of UCC, which is Japanese, although the Marcon name might have been owned by a different company in the past I suppose.

    Also, I don't think I've ever seen a component marked ".1" of anything; it's always "0.1".

    The M marking probably means ±20%.

    Since it's marked with a DC working voltage, it's probably electrolytic, and electrolytics are polarised. There is a black stripe around the body, indicating what would be the negative end, but you said you think both wires came out of the same end ("radial" rather than "axial" style), so I'm not sure what to think.

    Also, axial electrolytics usually have a "waist" near the positive end to hold the rubbery end plug in place. Radial electrolytics also normally have a waist near the plug end where the wires emerge. That one doesn't have a waist at all. This makes me think it may not be an electrolytic.

    It could be useful to see some more pictures from different angles. There are more markings that might give us more clues, and I would like to see both ends as well. And can you include a ruler in a photo, or tell us the approximate dimensions of it.

    Also since you know where it used to connect, can you show us a close-up of that part of the microscope base so we can see how it is connected in the circuit?
     
  6. jpanhalt

    jpanhalt

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    Nov 12, 2013
  7. duke37

    duke37

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    Jan 9, 2011
    It is not an electrolytic capacitor, it is far too big for that. I would think that it is too small for 1µF so would say 0.1µF.

    As has been said there are X and Y rated capcitors for use on the mains. I do not see where you have stated the mains voltage or frequency.
    If you have 250V mains, the voltage will peak at 355V and there will be transients on top of this. If you use a DC capacitor you should double the voltage rating to cater for the current passing in and out of the capacitor so a 1000V DC capacitor. A capacitor with AC rating would be better.

    If the potentiometer is to control the light level, then the bulb can be protected by not running flat out. If the meter does not work, then there is a fault which may be allowing excess voltage to the bulb.
     
  8. Bruce Taylor

    Bruce Taylor

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    Feb 2, 2014
    Thanks for the thoughtful informative replies, everyone. Sorry for my slow response...snowed in with work today.

    I think the capacitor shell is still at our old house (now our "country" home), and I will try to retrieve the next time I'm there. As I recall, it was a bit under an inch in length, and a perhaps 5/16 of an inch in diameter.

    Steve, thanks for the link. I did not know about X and Y rated capacitors.

    Kris, I was wondering the same thing about that blurry decimal. I think Marcon would be Japanese, as you suggest (Olympus certainly is). I'll take a couple more pics of the base, when I have a chance, and will post them.

    Jpanhalt, "metallized paper" does describe the confetti that flew from the exploded end of this thing: :)

    Duke, thanks for the additional info. I'd been vaguely thinking that the faulty capacitor was responsible for the dead voltage meter...but maybe that's illogical. What I know about electronics wouldn't fill that little grey tube, I'm afraid.
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Bruce, what's your location? (You can put this in your profile; it can be helpful for us to know). And what's your mains voltage?
     
  10. Bruce Taylor

    Bruce Taylor

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    Feb 2, 2014
    Kris, I'm in Canad (Ottawa). I've added that to my profile. :)
     
  11. electro_pa

    electro_pa

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    Aug 14, 2011
    My guess is that capacitor is a spark suppressor across the power switch or transformer. Used to suppress the large transients coming from collapse of transformer magnetic energy. These may be getting to the lamp and doing damage as you suspect. I would be adding a 275 volt varistor across the tranny primary as well.
    regards,
    Clive Judd.
     
  12. Bruce Taylor

    Bruce Taylor

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    Feb 2, 2014
    Thanks for the helpful information, Clive
     
  13. ap2wf

    ap2wf

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    Mar 21, 2014
     
  14. ap2wf

    ap2wf

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    Mar 21, 2014
    Hi.
    On the second picture the capacitor brand written is Rubycon, which is a Japanese brand of late 60s. The capacitor is oil filled and polarised. However, it should be of more priority and importance to confirm, whether you moved from 120 VAC to 220 VAC utility supply area, and also what is the microscope recommended operating voltage. I had a similar experience long ago. Equipment with low voltage step-down necessarily does not fail immediately at switch-on and withstands a higher voltage for a limited length of time.
    Good luck..
     
  15. JamesW

    JamesW

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    Jan 26, 2015
    Hi Bruce, I hope you are still picking up messages on this thread. I, too, have just had the capacitor blow on my Olympus EHT. The capacitor is identical to the one in your photograph. What did you end up replacing it with? Best regards, James
     
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