So in this video today we are going to look
at what a capacitor is, how it works, what it does, how to identify a bad cap and what
happens when they do go bad, how to find a replacement and how to install it. So capacitors
were originally known as condensers, so if you hear some of the old timers talking about
a condenser, you know what it is. Basically they are used to store a charge. They are
able to get rid of that charge very quickly, unlike a battery which is able to do it slowly,
these can do it instantly. In a power supply, generally you are going
to see aluminum caps like this and possibly some of the polyester style like that. Generally
they are going to be used for filtering out DC, because they allow AC to pass through.
Or they are going to be used to help filter and to steady DC voltage going out to the
main board or the T-con. What happens when a capacitor goes bad?
Capacitors are affected by temperature and voltage, if they are rated for a certain voltage
like this one is rated for 35 volts and you happen to expose it to a higher voltage, you
may find that the cap starts to fail prematurely. Also, the temp can cause it to fail prematurely.
When they begin to fail, they may start to produce gas inside of them which will result
in the tops becoming puffy. If its bad enough the top will burst open and allow the dielectric
inside, the insulating layer to ooze out. So often you will see a brown substance on
top of the cap and sometimes on the board as well. Certain capacitors if they happen
to fail spectacularly can actually blow the casing completely off and you will be left
with something that looks like that on the board and you will see kind of like a paper
outside and the little rubber stopper on the bottom and not much else.
In some TVs, some power supplies you will see that all the time and they will blow completely
off the board. So here we have a few examples of bad caps.
As you can see the tops in these have blown open and some of the dielectric has oozed
out from the inside. That happens just with the heat that gets generated inside the cap
when it starts to short out and fail. This one here is close, the tops puffy, but it
hasn't actually blown open yet. Again, this one will be bad and if you saw that on your
board you would need to replace it. The common issues with bad caps tend to be the TV not
powering on, the TV powering on, but taking multiple attempts. The multiple attempts will
probably take more and more as time goes on and the cap starts to dry out even more.
Usually once the TV comes on its going to function normally, but again once you power
it off and try and turn it back on, you are going to get those issues where it does not
want to start up. The other kind of capacitor that you will see used on inverters or sometimes
on power supplies that have high voltage sections on them going out to lamps are these little
ceramic capacitors. These are often used for feedback from the lamps and if those go bad
they generally don't go puffy like an aluminum caps, like these. What they are going to do
is usually show a burn spot or they can crack and fracture. If those go bad, generally it
acts like a bad lamp, the TV may come on briefly and then the backlights might shut off, the
rest of the TV could stay on but your backlights are going to turn off.
If your backlights turn off, make sure that you check these caps. If you see any burn
marks, or spots, anything like that. It is worth replacing them, make sure that you use
the same voltage and capacitance. They are really picky on these little feedback circuits.
If you do not put the right one in, it won't work.
This style here, the one with the polyester cap or teflon cap, generally these do not
go puffy, but you will see burn marks and sometimes will see the one side will become
kind of extended or bubble up more, just because there is more heat generated there. Again
they are usually pretty easy to spot. Check for burn marks and cracks in the cap. Identifying bad caps:
As we just mentioned bad caps usually show up with puffy tops and we have an example
right here. This one right here. And you can physically feel it, if you are not sure, you
can kind of compare it just by running your fingers over the top. Sometimes they can be
a little confusing, the little cross hatch patterns on the top can sometimes make it
look almost like it has a bump, but if you run across multiple, you will feel that one
definitely has a raised top. As you can see on this one it has started
to actually open up. There is a little brown spot. Sometimes if the TV is running, you
will actually get smoke or steam pouring out of these as they start to heat up and dry
out and start to short. Sometimes the casings will blow off and it will look like that,
it will just be the inside, which is usually some kind of cardboard or paper inside of
there right between the two layers of aluminum. For testing, if you only have a multimeter,
usually you are going to have to take the cap off the board to make it work properly
to check the cap. If its on there and there are other capacitors near by or resistors,
it can affect the results. So if you remove it, that is the best way to check. We have
set our meter to capacitance and we are going to put a probe on each leg and see what it
reads. Right there it is reading about 270 or so and dropping. If we look at this cap
its meant to be 680mf, so we know that it is defective. Usually your capacitor is not
going to read exactly what it says on the label. Often times there is about a 10-20%
difference between the actual marked value and what you are going to read. If its within
that, you should be fine. If its anything more than that, then you are going to want
to replace the capacitor. So another way to check for bad caps is to
use and ESR meter. This is used to check in circuit for bad caps and can pick up bad caps
that are not visible to the naked eye. A good cap, when you check should ring and
drop all the way down to 0hms pretty much. A bad one on the other hand, this is our puffy
one from earlier shows only that it is just good and doesn't beep at us. This one we know
if bad because of the puffy top. This one should look really bad, this one is the one
that blew. Yes and it shows in the bad range and barely moves.
So here we have a board and we can actually use the cap checker right on the board. We
are going to try this one and this one comes up as compare. Well we can look around the
board and try different caps. Lets try this one right here. That one is definitely good.
So we can be pretty sure that this one is bad and then we would go ahead and we would
pull the cap and check it using our regular multimeter and check the capacitance and replace
it if it is defective. So, a lot of people are probably not going
to have an ESR meter its one that generally techs are only going to have or serious hobbyists.
If you have got a multimeter though, you can use it to try and check caps in circuit, but
one of the issues you are going to have is when multiple caps are on the same set of
trace. So right here, we have these two 1500mf caps and I am going to flip it over and going
to try and read the value for one of the caps. OK, so we have our multimeter here and we
have it set in capacitance mode and we are going to try and measure the value of one
of the caps. We are going to take our probes and put one on each lead and then it will
autorange and go through and should give us the value. It is coming up as 3 millifarads
which is 3000 microfarads and we know from turning the board over that this cap should
be 1500 microfarads. The reason we are getting the wrong value is that we have these two
caps in parallel. Unlike resistance, when you put caps in parallel, they add together.
So, if you get a reading that you are not sure of, make sure that you check and see
if there are any other capacitors on that same line that are together in parallel. Make
sure you add the values together and that should tell you if your reading is correct.
Since we have the two 1500microfarad caps in parallel it should be reading about 3 millifarads
or about 3000 microfarads and that is exactly what we got on the reading. So we know that
these caps are good. Thank you for watching one of our many tutorials here at Shopjimmy.com.
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