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Name that capacitor

Discussion in 'Electronic Basics' started by Phideaux, Apr 22, 2004.

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  1. Phideaux

    Phideaux Guest

    I'm trying to repair a NAD 3140 amplifier which has had a couple of
    components burn out. The resistor that burned was identified by
    looking at the mirror side of the amp. but the cap that was burned is
    still a mystery. The markings are 104 EAE. There are many of these
    in the circuit, but I have no capacitor checker, so I'm still in the
    dark. Can anyone identify this cap value for me?
     
  2. My guess would be that this is a code for picofarads much like the
    resistor color code:

    10*10^4 = 100,000 pf = .1 uf

    You should be able to guess an appropriate voltage rating by what else
    is in the circuit.
     
  3. Tom Biasi

    Tom Biasi Guest

    John always gives very good info, but why did these components burn out?
    You need to know.
     
  4. I assumed that they were overheated by nearby burning resistors.
     
  5. UncleWobbly

    UncleWobbly Guest

    Capacitors like this are measured in pecofarads. 104 is a ten followed by
    four zeroes so the value is

    100,000pf, or 100nf. Peculiarly among capacitors, it seems popular to ignore
    certain SI number ranges, so people say things like "a thousand pecofards"
    when it should really be "1 nanofarad" down to common practice of grouping
    numbers in thousands. In restistors, you don't often hear "22 thousand
    Kilohms" it is of course 22 Meg... I wonder why? doesn't matter much but
    that capacitor you have there would commonly be described as :

    100nF
    or 0.1uF (microfarads)

    I assume you can identify what type of capacitor it was beyond it's value?
    There are many different ways to construct a capacitor and they all have
    varying electrical properties, mylar, ceramic disc, polyester, tantalum
    etc... this can be an important consideration in the particular application,
    ceramic disc tend to be quite "loose" tolerance, 20% of value is common, but
    where they are used to remove high-speed spikes from power rails, this
    tolerance isn't terribly important, but if it were in a timing circuit or in
    your case, an Amp, you need to know exactly how the beast is going to
    perform.
     
  6. Phideaux

    Phideaux Guest

    You guys are a riot! Tom, you are right on the spot. John, actually
    I think the capacitor shorted and the rush of dc current through the
    resistor let the smoke out of it and the capacitor. These two element
    are in series and feed one of the power output transistors. The
    capacitor (a ceramic disk) had one side burned off, complete with
    ashes still stubbornly clinging on. It was the side opposite of the
    resistor/capacitor connection. My novice appoach to trouble shooting
    told me that this should be considered in my analysis. My novice
    approach to repair will be to purchase two resistors and two
    capacitors, replace the pair, and see if the smoke stays in them when
    the switch is turned on. I did find two 15 amp fuses blown in the
    power supply circuit, and two 1 amp fuses blown elsewhere. I replaced
    these before taking out the charred and smelly elements, and their
    little flashes of light remained in them.
     
  7. ~^Johnny^~

    ~^Johnny^~ Guest

    Oh, jeez...
    --
    -john
    wide-open at throttle dot info

    ~~~~~~~~
    "The first step in intelligent tinkering is to
    save all the parts." - Aldo Leopold
    ~~~~~~~~
     
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