I am wondering if there is a technique for testing circuit board mounted electrolytic capacitors in (or out of circuit if nessecary) using a multimeter?
I may have a few bad caps on my amp. somewhere on my board and wondering the best way t test useing a dmm
anyone please advize? best way to test them with a dmm?
Thanks
I may have a few bad caps on my amp. somewhere on my board and wondering the best way t test useing a dmm
anyone please advize? best way to test them with a dmm?
Thanks
Not really.
What makes you think you have faulty caps? If I have a problem like this, I normally swap out all of the electrolytics in one go. After all, if one has reached the end of its life, then its likely the rest are nearly there as well.
What makes you think you have faulty caps? If I have a problem like this, I normally swap out all of the electrolytics in one go. After all, if one has reached the end of its life, then its likely the rest are nearly there as well.
Hi mrsmith,
Pinkmouse is right. A multimeter may tell you about a complete failure, open, short or very leaky. That's all. There are some ESR meters that can give you some of the story. I use a combination of HP 4263A ($$$$$), older cap checkers that apply high voltage and common sense.
Like pinkmouse said, "if in doubt, take them out"! Well, I said that, but it's cheaper to replace them when they are old rather than worry about it too much. That's where he was going.
Remember one thing, caps need to be pulled out of circuit to check them in any meaningful way, may as well stick a new one in.
-Chris
Pinkmouse is right. A multimeter may tell you about a complete failure, open, short or very leaky. That's all. There are some ESR meters that can give you some of the story. I use a combination of HP 4263A ($$$$$), older cap checkers that apply high voltage and common sense.
Like pinkmouse said, "if in doubt, take them out"! Well, I said that, but it's cheaper to replace them when they are old rather than worry about it too much. That's where he was going.
Remember one thing, caps need to be pulled out of circuit to check them in any meaningful way, may as well stick a new one in.
-Chris
oh ok thanks for the advice,
can i ask a quick question, i have some exect caps same uf and voltage,
the origanal caps in amp are blue bodied cans, but the spare ones i have are black bodied cans.
is there a diffrence or not?
thankyou
can i ask a quick question, i have some exect caps same uf and voltage,
the origanal caps in amp are blue bodied cans, but the spare ones i have are black bodied cans.
is there a diffrence or not?
thankyou
Hi mrsmith,
No difference, just a different make. Just as long as you haven't had them in storage since the Seventies!
Go ahead and use them. Mind the polarity.
-Chris
No difference, just a different make. Just as long as you haven't had them in storage since the Seventies!
Go ahead and use them. Mind the polarity.
-Chris
yes, you can do it, but not with multimeter, you need so-called in-circuit ESR meter, which measure the series resistance (best models measure it at several frequencies). The usual elco failure is not capacitance loss, but substantial increase in ESR with time...
I'm sorry dimitri,
I have to disagree with you. In circuit testing will not show leakage when it occurs. Circuit effects may change other readings too.
The only way to test capacitors (or any other component, save a fuse maybe) is out of circuit. It's the only way you can be sure of your reading. What happens if there is another cap in parallel somewhere else?
-Chris
I have to disagree with you. In circuit testing will not show leakage when it occurs. Circuit effects may change other readings too.
The only way to test capacitors (or any other component, save a fuse maybe) is out of circuit. It's the only way you can be sure of your reading. What happens if there is another cap in parallel somewhere else?
-Chris
Before acquiring my cap/ind meter, I checked cap in the following way:
1. Voltage range
Put a suitable resistor in series with the cap and the power supply. Crank the voltage up slowly and observe the current into the cap. The current should come down to a very low level(leakage current) when the cap is fully charged up. If the current is still high for sometime, you got a leaky cap. Toss it.
2. Capacitance check - a very rough method.
I prefer to use analogy meter to do this. Switch the meter to ohm range. Which range to use is depending on the capacitance. Connect the +ve test probe to the +ve terminal of the cap, negative probe to the negative terminal. The initial reading should be zero as the cap is at short-circuit state. The meter needle will then move slowly towards the high resistance reading and eventually at infinite. You can use this technique to compare the cap you want to test with another known good one of known value. The needle movement speed difference will give you a good idea the capacitance difference.
Hope this helps.
1. Voltage range
Put a suitable resistor in series with the cap and the power supply. Crank the voltage up slowly and observe the current into the cap. The current should come down to a very low level(leakage current) when the cap is fully charged up. If the current is still high for sometime, you got a leaky cap. Toss it.
2. Capacitance check - a very rough method.
I prefer to use analogy meter to do this. Switch the meter to ohm range. Which range to use is depending on the capacitance. Connect the +ve test probe to the +ve terminal of the cap, negative probe to the negative terminal. The initial reading should be zero as the cap is at short-circuit state. The meter needle will then move slowly towards the high resistance reading and eventually at infinite. You can use this technique to compare the cap you want to test with another known good one of known value. The needle movement speed difference will give you a good idea the capacitance difference.
Hope this helps.
Chris, leakage is parallel resistance to cap, I'm speaking about the series one ...
http://www.fullnet.com/u/tomg/esrscope.htm
http://www.e-repair.co.uk/tipsgeneral101.htm
http://ludens.cl/Electron/esr/esr.html
http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/fig03.gif
http://personalpages.tds.net/~rcarlsen/ce/esrmeter.txt
http://www.fullnet.com/u/tomg/esrscope.htm
http://www.e-repair.co.uk/tipsgeneral101.htm
http://ludens.cl/Electron/esr/esr.html
http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/fig03.gif
http://personalpages.tds.net/~rcarlsen/ce/esrmeter.txt
Hi dimitri,
Yes, I know. ESR is but one failure mode. Mostly a low voltage thing. High voltage caps can to either or both, leakage is dangerous.
My point is simply that you can't accurately know a component is good or bad in circuit. I've been burned too many times by believing what others claim to be true. Over 30 yrs. experience has shown me that you can't take shortcuts.
Putting my $$ where my mouth is, I bought an HP 4263A - new, with three sets of leads. It's my second one (the first was an HP 4261A). This is after using the other so called capacitor testers. I didn't spend that money because I like to spend. It was needed for what I do.
The other testers (ESR, etc ..) found some bad caps. The HP finds more. What the HP doesn't catch, a meter with HV supply and high resistance (220K) finds. The only thing I check in circuit is leakage in tube circuits. Well, I lied, I look for ESR on supply caps with a 'scope while the unit is in operation too.
-Chris
Yes, I know. ESR is but one failure mode. Mostly a low voltage thing. High voltage caps can to either or both, leakage is dangerous.
My point is simply that you can't accurately know a component is good or bad in circuit. I've been burned too many times by believing what others claim to be true. Over 30 yrs. experience has shown me that you can't take shortcuts.
Putting my $$ where my mouth is, I bought an HP 4263A - new, with three sets of leads. It's my second one (the first was an HP 4261A). This is after using the other so called capacitor testers. I didn't spend that money because I like to spend. It was needed for what I do.
The other testers (ESR, etc ..) found some bad caps. The HP finds more. What the HP doesn't catch, a meter with HV supply and high resistance (220K) finds. The only thing I check in circuit is leakage in tube circuits. Well, I lied, I look for ESR on supply caps with a 'scope while the unit is in operation too.
-Chris
Hi Andrew,
I have found that as a supply cap become less effective, the high frequency components are not filtered out. This results in a "pip" on the leading edge of the waveform. The worse condition the cap is in, the bigger the"pip". The waveform is normally roughly triangular.
The bigger electrolytics can have a small tip on the leading edge. I think the worst ones were massive. They were in a Bedini, they went from from to back. Even good, these had such inductance that they had ripple while the amp modules were pulled! Not good taken to extremes (like most things).
Anyhow, this is reasonably reliable, and confirmed with my HP 4263A. Obviously a normal sized cap on light load with high ripple is bad.
Have you seen similar things?
-Chris
I have found that as a supply cap become less effective, the high frequency components are not filtered out. This results in a "pip" on the leading edge of the waveform. The worse condition the cap is in, the bigger the"pip". The waveform is normally roughly triangular.
The bigger electrolytics can have a small tip on the leading edge. I think the worst ones were massive. They were in a Bedini, they went from from to back. Even good, these had such inductance that they had ripple while the amp modules were pulled! Not good taken to extremes (like most things).
Anyhow, this is reasonably reliable, and confirmed with my HP 4263A. Obviously a normal sized cap on light load with high ripple is bad.
Have you seen similar things?
-Chris
Andrew T and Company,
Greetings and hi there from Kuwait.
About the various kinds of cap testing tools out there.
Units that measure uF are nice, but I have made a lot of money with an ESR meter.
I got clued into this instrument when I was working in the Video Game industry. Switch mode power supplys and video displays beat the tar out of elytic caps.
With the ESR meter and a marking pen I was able to go through a monitor and pick out all the bad caps over .5uF and have all the cap related monitor faults solved after replacing.
I even purchased a second meter for use here in Kuwait fixing Army electronics.
So if you do a web search on video monitor repair and ESR meters, you will find one made by Independance Electronics in the USA. It's about 200 bucks, and it will be some of the best two hundred bucks you can spend.
It's not a total cure all.
For example if there are three caps in parallell, it can be faked out.
I also use mine for low ohms testing. Very handy for some items here.
Much luck and be well
Jack Crow
Kuwait City
Greetings and hi there from Kuwait.
About the various kinds of cap testing tools out there.
Units that measure uF are nice, but I have made a lot of money with an ESR meter.
I got clued into this instrument when I was working in the Video Game industry. Switch mode power supplys and video displays beat the tar out of elytic caps.
With the ESR meter and a marking pen I was able to go through a monitor and pick out all the bad caps over .5uF and have all the cap related monitor faults solved after replacing.
I even purchased a second meter for use here in Kuwait fixing Army electronics.
So if you do a web search on video monitor repair and ESR meters, you will find one made by Independance Electronics in the USA. It's about 200 bucks, and it will be some of the best two hundred bucks you can spend.
It's not a total cure all.
For example if there are three caps in parallell, it can be faked out.
I also use mine for low ohms testing. Very handy for some items here.
Much luck and be well
Jack Crow
Kuwait City
Hi Jack,
You are right. You understand your insturment and that's important.
I didn't say those didn't work, my main point is that to be somewhat sure, the component has to be out of circuit. This can at least get you in the ballpark to start checking.
-Chris
You are right. You understand your insturment and that's important.
I didn't say those didn't work, my main point is that to be somewhat sure, the component has to be out of circuit. This can at least get you in the ballpark to start checking.
-Chris
mrsmith said:
My Fluke #29 DMM has a capacitance function. I always test mine out of the circuit.
Hi BoomBoomBoy,
The capacitance function on a Fluke is pretty good for reading the value of the cap. Keep in mind you are not measuring DA, leakage or ESR. You can detect when there is something very wrong with the cap you are testing.
Great for testing new capacitors that are known good.
-Chris
The capacitance function on a Fluke is pretty good for reading the value of the cap. Keep in mind you are not measuring DA, leakage or ESR. You can detect when there is something very wrong with the cap you are testing.
Great for testing new capacitors that are known good.
-Chris
anatech said:
You're right, thanks! I remembered it only read values after I posted. I don't use that fuction very often. My bad.
Hi BoomBoomBoy,
Not your bad. You were pointing out a function in the spirit of the thread. I feel it was worthwhile input.
-Chris
Not your bad. You were pointing out a function in the spirit of the thread. I feel it was worthwhile input.
-Chris
Hi guys,
This meter is hard to fake out but it can be done.
First off it's an AC ohmmeter.
The test signal is 100khz at about 3mV
Not enough to kick over a diode junction, but more than enough to work on resistive and cap loads up to about 30 ohms.
It's also a four wire kelvin measurment. So wire leingth is compensated.
Later guys
Jack Crow on R and R in Vegas.
This meter is hard to fake out but it can be done.
First off it's an AC ohmmeter.
The test signal is 100khz at about 3mV
Not enough to kick over a diode junction, but more than enough to work on resistive and cap loads up to about 30 ohms.
It's also a four wire kelvin measurment. So wire leingth is compensated.
Later guys
Jack Crow on R and R in Vegas.
I would say that 99% of low-voltage electrolytics can be tested in-circuit with good esr-meter. With high-voltage ones results vary, as you said they may leak instead of rising esr.anatech said:
Have to agree what you say about Fluke multimeters, its useless for finding dried electrolytics, in-circuit or not.
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