# Name that capacitor

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

1. ### PhideauxGuest

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. ### John PopelishGuest

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 BiasiGuest

John always gives very good info, but why did these components burn out?
You need to know.

4. ### John PopelishGuest

I assumed that they were overheated by nearby burning resistors.

5. ### UncleWobblyGuest

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

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. ### PhideauxGuest

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^~Guest

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

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