Question about blown capacitors (non audio related)

If a capacitor is leaking or bulging in any direction, it's dead.

If you want to get fancier than that, you need both a capacitance meter (frequently available as a feature on multimeters these days) and an ESR meter.

An ESR meter measures the Equivalent Series Resistance of a capacitor, which is measured in micro-ohms. It's generally a single-function device, and AFAIK the cheapest one out there is available in kit form for about $85. Google "Blue ESR Meter" for more info. Basically, if a capacitor has a relatively high ESR, it's probably on it's way out. Generally speaking, if the caps are drained, you can use an ESR meter while the cap is still in the circuit.

It helps sometimes to look up the datasheet for the dead capacitor and select a replacement that has a similar esr, surge rating, and tangent of loss. And sometimes it doesn't really matter as long as you're in the same ballpark.

Get the same or higher voltage, same capacitance rating, same or higher temperature rating.

105c is as high as you get for most caps.

If this is the 2nd time they've needed replacing i wonder if the heat is the only problem, though.

Those caps are listed as "general purpose" and you might benefit from "low impedance" in this application. Or you might not. Hard to say without knowing the circuit pretty well.

You might want to check the voltage rating of the cap against the actual measured voltage in the circuit.

Maybe the caps are being run too close to their rated voltage. You might want to try the next higher

voltage rating for that cap.

You seem to be on the right track. Larger caps with same ratings will possibly be more reliable due to heat dissipation. On another note, if the bad cap is rated for 16 volts, a 25 volt cap may work for a longer period.

No, measure the voltage across the leads of the cap.

Capacitors are made from layers of a conductive film

and an insulating film. The voltage rating is the point

where the insulating layer breaks down. When the

voltage rating is exceeded, the usual result is that the

cap does something nasty like explode or catch fire...
 

Quote:

Originally Posted by BobSaysHi 

I really don't know what I am doing, and that is above me. I don't think any voltage is going through, since the monitor doesn't turn on. Wouldn't I need working capacitors to measure the voltage? 

 

EDIT: Nevermind, I understand what you are saying, but I still don't know how to do it. would I just put my multimeter to the negative of the capacitor and then measure the other end to ground? 

 

I can understand that these are broken and need replacing, but I don't know why. I am trying to learn though.

It looks like more than one cap has failed. Maybe it's the lighting in the picture

but it looks like three of the caps have failed. That would tell me there is something

definitely wrong with the circuit. Replace the caps with the same uF value but one

voltage level higher rating. Once the circuit is up and running again measure the voltage

across the leads of the caps. I will bet they are very close to the rated value of the

failed caps. Also, there is a ribbon cable leaving the board on the bottom right. It looks

like there is a table of signals for it. Check the voltages listed in the table to see if they

are correct. If they are all too high then there is a problem with the AC regulator side

of the power supply.

I'll give you a quick and dirty description of what is on the board...

The line AC comes in at the connector near the left center (pretty obvious)

and the two grey box caps and the smaller transformer beside them form

a low pass filter to filter noise from the AC line. The AC is then "regulated"

by the other circuitry in the bottom left of the board. This AC is then passed

through the main transformer (the "yellow box") for the monitor to use.

The white line that passes under the main transformer shows you which side

is live AC and which side is (for lack of a better word) the safe side.

The blue rectangle at the top center is probably the DC/DC converter that

generates the higher voltages for the back light tubes.

Quote:

Originally Posted by BobSaysHi 

Ok, I've been reading for a little while, and I'm piecing everything together in my mind. Please correct me if I am wrong.

 

Capacitors regulate voltage from a circuit. They store the voltage of the source, and absorb/release voltage depending on the voltage flowing through it to create a consistent voltage from a variable voltage.

ehhh, sort of.

A capacitor is a bit like a battery that can charge and discharge really fast. In fact, the more battery and capacitor technologies advance, the blurrier the line between them gets - including stuff like lead-acid batteries where the lead is a fine mesh coiled up just like a capacitor. 

Capacitors have low AC impedance but very high DC impedance. This means that, in a power smoothing application, you put one leg on the powered side of the circuit and one leg on the ground side.

And now i'm going to mangle science by using a water analogy.

Lets say that for some reason you need a constant stream of water down a hole somewhere and your only source of water is waves lapping up on a beach.

So you dig a channel that allows some of the wave water to trickle down into the hole - but since it's coming from waves, you get spurt after spurt after spurt, and this is no good for your application.

To smooth the flow of the water, you might install a small bucket with a hole in it as an intermediary stage. The wave fills up the bucket, and the bucket gives you a more constant trickle of water.

Except that's really closer to how an inductor works.