General electronics question...

Doward

[H]ard|Gawd
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Jul 3, 2004
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How can you tell (generally) when a capacitor is blown? Don't they usually bulge out at the top?

Generally speaking, can a cap be bad, and not display any outward signs?
 
Signs of a blown capacitor. Bulging at side top or bottom, leaking, and/or discoloration. And yes they can be bad without showing any of these signs.
 
Would a decent multimeter be able to check caps, without removing them from the PCB? As in, is there a certain ohm value or something that a cap should have? I've seen the 470mf and 1000mf caps, but am unsure exactly what a 'mf' is :)
 
Yes, but only to tell if it's bad or good not to tell the uF rating. Just test the resistance of it. If it reads infinite it's good, if it shows low resistance it's bad. Hold the probes on there for a little bit though because it will have to discharge. And a mf is a Micro Farad.
 
Doward said:
Would a decent multimeter be able to check caps, without removing them from the PCB? As in, is there a certain ohm value or something that a cap should have? I've seen the 470mf and 1000mf caps, but am unsure exactly what a 'mf' is :)

Ok, this is one of the few areas high school physics apply:
m = 10^-3
u = 10^-6
n = 10^-9
p = 10^-12

So a 470mF cap has a capacitance of .470 Farad. A 1000mF cap has a capacitance of 1 Farad (a HUGE cap, btw).

In answer to your question, the cap has to be removed from the circuit board in order to accurately test it. When the cap is soldered to the board, you have no idea what its connected to. More than likely its connected to an IC, in which case, you have no idea what's inside the chip. If there's another cap, in series or parallel to the cap in question, a meter would give you the wrong value. The same holds true to resistors as well. I learned this the hard way. I was debugging a ciruit and wanted to check if there were shorts between +12V power and ground. So I checked if there was any resistance between the 2 potentials. My meter would fluctuate between like 10Kohms and 0L (no continuity). After days of trying to find the problem, I learned that an IC on the board has an internal cap that goes from +12V to ground. This is what my meter was reading. So yes, you have to remove components from the board to check their values.

Anyways, I would recommend not doing this yourself. Its very difficult to remove components from a mobo, and even more difficult soldering them back on. If you believe a cap is busted on a mobo, simply RMA it. The cost of an RMA should be much less than the cost of a new board.
 
Sirje31337 said:
Yes, but only to tell if it's bad or good not to tell the uF rating. Just test the resistance of it. If it reads infinite it's good, if it shows low resistance it's bad. Hold the probes on there for a little bit though because it will have to discharge. And a mf is a Micro Farad.

You could try that, but there's still no garuantee that the cap has the right capacitance. Oh and mF is NOT a microfarad. uF is a microfarad. Remember that u is pronounced "mue".
 
Actually, it's not a mobo - it's a TV that was just given to me. :)
 
joecool234 said:
Ok, this is one of the few areas high school physics apply:

I was under the impression that physics and its governing laws applied to the entire universe. Maybe I was mistaken...
 
Then why would you think a cap went bad? Is the TV not working? The only reason I ask, is that TV repair is undoubtedly the MOST dangerous of all electronics repair. The tube holds enough charge to through you across the room, through a wall, and into the next room. No TV is worth being reduced to a bloody pile of mush.
 
Add 'em said:
I was under the impression that physics and its governing laws applied to the entire universe. Maybe I was mistaken...

The reason I said "high school" was that NY state's regents high school course is just flat out wrong. Anyone that took physics in NY can attest to that...I was taught that current flows from - to +.....left hand rule instead of right hand rule....should I go on?
 
The screen itself is rather shaky - like the vertical lines are having trouble staying 'vertical' LOL

It gets worse, the more 'data' on the screen.

It's a 53" Sony KP53V45 projection screen, and has been unplugged for about 3 days now. I know they can hold a heck of a bolt, so I'm being careful with it.

I'm picking up a service manual in the next couple of days - I have a feeling a couple of caps on the board around the frame IC are bad, though - just never tested caps before :)
 
joecool234 said:
The reason I said "high school" was that NY state's regents high school course is just flat out wrong. Anyone that took physics in NY can attest to that...I was taught that current flows from - to +.....left hand rule instead of right hand rule....should I go on?


WTF. Actually, yes. OMG. - to + , eh? ;)
 
joecool234 said:
The reason I said "high school" was that NY state's regents high school course is just flat out wrong. Anyone that took physics in NY can attest to that...I was taught that current flows from - to +.....left hand rule instead of right hand rule....should I go on?

Fair enough.
 
Doward said:
The screen itself is rather shaky - like the vertical lines are having trouble staying 'vertical' LOL

It gets worse, the more 'data' on the screen.

It's a 53" Sony KP53V45 projection screen, and has been unplugged for about 3 days now. I know they can hold a heck of a bolt, so I'm being careful with it.

I'm picking up a service manual in the next couple of days - I have a feeling a couple of caps on the board around the frame IC are bad, though - just never tested caps before :)

Ok, I take back what I said about the CRT tubes...you don't have one.

I can say that I know nothing about projection tv's as far as safety is concerned. Have you tried to find a replacement board? Check ebay/google. That's where I would look first. Then try Sony...all before trying the mod yourself.
 
Two notes here...

Current (in a typical conductor at least) does flow from - to +, since electrons are acting as the charge carriers, it's merely by common convention that most books and schools teach it backwards. So a purist will have a perfect right to decry those who use the antiquated + to - convention. It turns out that it doesn't really matter which way you use if you're consistent.

mF technically means a milli Farad, or 1/1000 of a Farad, but in reality it usually means a micro Farad because it used to be fairly conventional to abbreviate micro with an 'm', and it still happens in some cases. Anything big enough to be measured in milli Farads will usually be listed in uF or as a fraction of a F anyway, ie 470mF would be listed as .470 F or 470,000uF.
 
joecool234 said:
The reason I said "high school" was that NY state's regents high school course is just flat out wrong. Anyone that took physics in NY can attest to that...I was taught that current flows from - to +.....left hand rule instead of right hand rule....should I go on?
Duh... current DOES flow from negative to positive. :rolleyes: Please, go on.
 
Do Projection TVs hold the same charges as a CRT TV? Im guessing not since the main danger part is the CRT itself.

Also mattg2k4 is quite correct along with everyone else who says its - to +, in my books - to + is called electron flow and + to - is called current flow........ i think.......they could be reversed.....:D
 
Most older projection tvs do indeed use CRTs. Often times 3 of them, in fact. They are considerably smaller than the CRTs in standard televisions, but they are there nonetheless, and should be treated with the same amount of respect. I don't know if this particular projection tv uses CRTs or some other technology, but it is something to pay attention to.
 
I love how a simple anecdote results into a completely off-topic rant. Say what you want. I know what I learned in NY state. I also know what I learned at Johns Hopkins University in Physics for Engineers...and the two courses in fact conflict. You know what? I had the same professor teach both regents physics and AP physics to me in high school. Day one of AP started with, "Remember what you learned last year, well, forget it...everything's reversed now." Anyone from NY want to attest to this?
 
joecool234 said:
The reason I said "high school" was that NY state's regents high school course is just flat out wrong. Anyone that took physics in NY can attest to that...I was taught that current flows from - to +.....left hand rule instead of right hand rule....should I go on?

current DOES actually flow from - to +... most technitions are taught this way too, and you'll see it on alot of schematics at certain websites... it's known as "Electron Flow"


However, for some reason, us engineers always use what's called "conventional current flow", where we say it flows from + to - ...basically, this is done simply by tradition. when electrical school of thought was in it's infancy, they assumed the current flowed from + to -... and well, they were wrong. basically all scematics, symbols, markings on parts, etc. are represented by conventional current flow (for example, diodes on schematics have an arrow facing the way current flows if using the + to - convention, and they have a line around the end on the physhical part indicating the arrow from schematics).

(sorry for getting so off topic there)
 
joecool234 said:
The reason I said "high school" was that NY state's regents high school course is just flat out wrong. Anyone that took physics in NY can attest to that...I was taught that current flows from - to +.....left hand rule instead of right hand rule....should I go on?

Current does flow from negative to positive. this is called electron current flow theory. It superceeded conventional current flow(+ to -) theory in the early 20th century the resons of which i have long forgotten. it doesnt really matter anyhow it just depends on how you want to look at you circuit. What matters is that current does flow.

Take a forward biased diodefor example: electron current flow , the arrow points into the current and moves back "opening" the valve and letscuurent past. If polarity is reversed and the diodes position hasn't changed the arrow moves foward with the current and "closes" the valve.

in conventional current flow the arrow simply points with the current flow when foward biased.

when i say arrow i mean the anode symbol for a diode.

hope this helps.
 
We can all thank none other than Benjamin Franklin for getting the whole current/electron flow thing backwards. He thought the charge carriers were positively charged. Now we know that the actual things moving are electrons, with a negative charge, going in the direction opposite of what Franklin thought. By convention, however, "current" still flows from + to -, while we smart people know that electrons go the other way. Except when you're dealing with semiconductors, in which case you DO have "positive charge carriers". But let's not get into that.

Yes, everything would be a whole lot easier if Benjamin Franklin had got it right the first time. But then, anyone could be an EE, and I'd have a lot more competition.

Anyway, back to the question at hand....if you're just wondering about one specific capacitor, why not just replace it with one that has identical specs, and see what happens? Worst case scenario--you replaced a good cap. But now you can test it, and if you're wondering about any other identical caps, you can swap them out with the one you just removed, if it's good.
 
Electrons do flow from negative to positive. But as long as you're not working with electrons themselves (designing transistors or whatnot...) it doesn't matter at all.

Anyway, to the thread starter... to check if a capacitor is bad, here's my way of checking:

1) remove it from the circuit first!
2) verify if it's shorted using a DMM
3) measure capacitance using a DMM, LCR meter, or whatever you have.
4) bring it up to its rated voltage and measure the leakage current.
5) reinstall if it's good.

Anyhow, what's wrong with the TV? the "sci.electronics faq" on repairfaq.org has an excellent guide on how to fix them.
 
but the charge carriers are negative so it goes plus to minus at the same time depending on how you're looking at it :p

things like this are why ME > EE

plot said:
current DOES actually flow from - to +... most technitions are taught this way too, and you'll see it on alot of schematics at certain websites... it's known as "Electron Flow"
 
Sirje31337 said:
Yes, but only to tell if it's bad or good not to tell the uF rating. Just test the resistance of it. If it reads infinite it's good, if it shows low resistance it's bad. Hold the probes on there for a little bit though because it will have to discharge. And a mf is a Micro Farad.

As stated it's milliFarad, but what I wanted to say is that your method of testing it won't work while it is in the circuit since it is connected to many other things.
 
gee said:
Electrons do flow from negative to positive. But as long as you're not working with electrons themselves (designing transistors or whatnot...) it doesn't matter at all.

Anyway, to the thread starter... to check if a capacitor is bad, here's my way of checking:

1) remove it from the circuit first!
2) verify if it's shorted using a DMM
3) measure capacitance using a DMM, LCR meter, or whatever you have.
4) bring it up to its rated voltage and measure the leakage current.
5) reinstall if it's good.

Anyhow, what's wrong with the TV? the "sci.electronics faq" on repairfaq.org has an excellent guide on how to fix them.

this is ridiculous I think.. if you are going to remove it just replace it..They are cheap. it's not even worth the time of testing it, especially if you may make a mistake and not replace it if it's bad.
 
aL Mac said:
this is ridiculous I think.. if you are going to remove it just replace it..They are cheap. it's not even worth the time of testing it, especially if you may make a mistake and not replace it if it's bad.
If you're working in a factory when you've got boxes and boxes of these parts and you're getting paid for your time, then replacing it makes a lot of sense.

But for the hobbyist who has plenty of free time but has to order most of the parts they need, it's often easier/faster to verify the part is OK than order everything new.
 
ya know... you guys have made a mess of this thread. start a new thread for the - to + debate!
and do you know how many times i have posted a question on a forum, and someone replies saying, "hey- wouldn't it be easier just to blah blah blah?". yeah of course it would be. but i wouldn't be here asking this question if i wanted to do it the easy way.
and i know you guys know how it feels to fix somethng. especially something so complicated...
and how do you learn how to do things unless you do them?? he should test the cap! then he'll know how to from now on. it's not a waste of time if he's learning something!
can't someone just provide him with some help?
 
ya know... you guys have made a mess of this thread. start a new thread for the - to + debate!
and do you know how many times i have posted a question on a forum, and someone replies saying, "hey- wouldn't it be easier just to blah blah blah?". yeah of course it would be. but i wouldn't be here asking this question if i wanted to do it the easy way.
and i know you guys know how it feels to fix somethng. especially something so complicated...
and how do you learn how to do things unless you do them?? he should test the cap! then he'll know how to from now on. it's not a waste of time if he's learning something!
can't someone just provide him with some help?

*applauds Kerri Ann* Nicely said.
 
That really makes a lot of sense. Throw away a perfectly good part and put in a new one?

aL Mac said:
this is ridiculous I think.. if you are going to remove it just replace it..They are cheap. it's not even worth the time of testing it, especially if you may make a mistake and not replace it if it's bad.
 
It's not that expensive.. probably not even at radio shack.. It will only cost a few cents and probably less time to go to radio shack and buy a capacitor. now if you had 50 to test that might be different but if it is just one in question just go replace it. It is the sure way to do it.
 
The only incentive to simply replacing the cap is a no-brainer. Once you remove the cap in question, take a look at the leads. I'll give 1000:1 odds that the leads are way too short to work with...you'll even have trouble testing the cap, because the leads are too short. Its up to you...once that cap is removed, I personally would just add another one. If you buy a 10 pack of caps, you can probablly get them for $.50 a piece. And resistance/capacitance isn't the end-all-be-all specs for testing caps. Just because the cap in question tests correctly, doesn't mean its still OK. Its just a good starting point. Would someone rebuilding an engine simply clean the rings...or would they replace them?

Kerri Ann said:
and do you know how many times i have posted a question on a forum, and someone replies saying, "hey- wouldn't it be easier just to blah blah blah?". yeah of course it would be. but i wouldn't be here asking this question if i wanted to do it the easy way.

Oh, and for the record...the OP's question has already been answered. Who is anyone to say that advice that doesn't answer the original question isn't wanted? The whole purpose of this forum is to provide help, assisstance, and advice. If replacing a capacitor is a simpler route than testing it so be it. To truly check the status of a capacitor, you need a lot more than just a DMM. Assanine comment.
 
joecool234 said:
I love how a simple anecdote results into a completely off-topic rant.
if you want to quote me, leave it in it's context. i wasn't aiming my comment at you. i was simply saying that many times when I ask questions about things, i receive advice on how to do it a different, easier way. but many times i asked the question because I want to know how to do whatever it is i'm trying to do, and why it works the way it works.
 
aL Mac said:
It's not that expensive.. probably not even at radio shack.. It will only cost a few cents and probably less time to go to radio shack and buy a capacitor. now if you had 50 to test that might be different but if it is just one in question just go replace it. It is the sure way to do it.
chances are, the caps you find inside a television set aren't available at radio shack... you'll probably end up placing a digikey order.

But before fingering bad capacitors, an understanding of the circuit that the cap is in is needed. The http://www.repairfaq.org site offers an excellent guide on repairing TV sets, and using this the thread starter should be able to track down a certain section of the TV that's causing grief.
 
gee said:
chances are, the caps you find inside a television set aren't available at radio shack... you'll probably end up placing a digikey order.

But before fingering bad capacitors, an understanding of the circuit that the cap is in is needed. The http://www.repairfaq.org site offers an excellent guide on repairing TV sets, and using this the thread starter should be able to track down a certain section of the TV that's causing grief.

Thank you, although I needed to check out one of the mirrors. Within 10 seconds of reading that link, my assumptions were correct. You need a lot more than a simple DMM to check the health of a cap. Read http://repairfaq.ece.drexel.edu/sam/captest.htm#cttes for example.

I apologize for forgetting the original intent of the thread starter. The caps for a TV board are probablly very large and quite costly to replace. Visual signs of damage are undoubtedly your first sign...check the above link for further testing instructions.

P.S. The first place I would look for cheap caps is Ebay. My boss was able to buy a LOT (100 denominations 2000+ qty) of resistors for less than $50. I'm sure you can find good deals on large TV electrolytics.
 
Ok, So you think a cap is bad. You remove it. It's fine. You have two options:
1) Put it back in.
2) Go to radioshack, buy a new one, put the new one in, throw away the perfectly good old one.

2 is a better option to you?

aL Mac said:
It's not that expensive.. probably not even at radio shack.. It will only cost a few cents and probably less time to go to radio shack and buy a capacitor. now if you had 50 to test that might be different but if it is just one in question just go replace it. It is the sure way to do it.
 
Whatsisname said:
Ok, So you think a cap is bad. You remove it. It's fine. You have two options:
1) Put it back in.
2) Go to radioshack, buy a new one, put the new one in, throw away the perfectly good old one.

2 is a better option to you?

I'm sorry you said "it's fine" I'm glad you are omniscient.

I would think you'd need to make your own circuit and have an oscilloscope to really test a capacitor.. no? So go blow several hundred dollars, get yourself some equipment and then buy yourself several more parts to build a circuit and you can test all the capacitors you want. Or.. you could of taken a 5 minute trip to the store bought some assorted parts that every electronics hobbyist should have laying around and just replace the capacitor in question.
 
aL Mac said:
I'm sorry you said "it's fine" I'm glad you are omniscient.

I would think you'd need to make your own circuit and have an oscilloscope to really test a capacitor.. no? So go blow several hundred dollars, get yourself some equipment and then buy yourself several more parts to build a circuit and you can test all the capacitors you want. Or.. you could of taken a 5 minute trip to the store bought some assorted parts that every electronics hobbyist should have laying around and just replace the capacitor in question.

Amen brotha...

This theory holds true for every piece of serviceable consumer equipment. A car is a great example. If just about ANY component on a car breaks, will the mechanic fix the broken part...or simply replace it? Sure, its cheaper to fix the broken part, but time is money also.

Fact of the matter remains, it is not a simple task to check the health of a cap. If the OP chooses to do this, more power to him. But in this situation, the "easier" route is the route most gauranteed to produce correct results.
 
Whatsisname said:
but the charge carriers are negative so it goes plus to minus at the same time depending on how you're looking at it :p

things like this are why ME > EE

it isn't too hard to think of why we first thought it flowed from + to - since most normal things move from higher potential to lower potential. For example a ball rolling down a hill. However even though we know electrons actually flow .. unless you are looking at the actual physical make up of transistors or other semiconductors it doesn't matter, as long as you pick a convention and make sure you stick to it.

Oh yeah EE > ME =]
 
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