in-circuit capacitor/resistor tester suggestions?
- Thread starter gogofast
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Rather pricey as well...
Testing any component in-circuit is always a compromise. Lifting one lead is always preferred, if doable. If not...
It is difficult to test the resistance of an in-circuit resistor with accuracy, because there will almost always be alternate circuit paths. So, here's what you can do: Using any quality DMM, read the resistance of the resistor under test, and compare with the marked value, including the +/- tolerance. If you read a value that is higher than the marked value, the resistor has probably drifted up in value, particularly if it's a high value resistor. If it's open, it's bad. If you read a value lower than the marked value, then you really can't tell if the resistor is good or not, because you could be reading the resistance of the alternate circuit path. Not a lot of help, is it.
The only accurate, reliable way to test whether or not a capacitor is functioning correctly is to both measure the actual capacitance and also to apply the capacitor's stated working DC voltage and check for current leakage. Obviously, putting two test leads on the cap while it's in circuit and pumping 630 VDC into your amp isn't something that anybody will ever do. Heaven knows how many things you'd fry. So, the next best way to test an in-circuit capacitor is with an ESR (Equivalent Series Resistance) tester. These are readily available, and the prices run from quite reasonable (<$100) to a lot higher (~$1,500) for a professional quality instrument. Kits are available, as well.
There are acceptable ranges of ESR based on the capacitance and voltage value being tested, and if it's out of range then it's probably bad. However, it could still be inside the acceptable ESR rating, but show leakage when under full operating voltage. An ESR tester only applies a tiny test voltage (in the mV range) to the capacitor during the test. Edit: One other thing, it's my understanding that ESR testing is only reliable for capacitors that are larger than 1 uF (approximately).
Some interesting links:
http://octopus.freeyellow.com/esr.html
http://ludens.cl/Electron/esr/esr.html
http://www.members.shaw.ca/swstuff/esrmeter.html
http://www.electronix.com/catalog/product_info.php/cPath/17_489/products_id/18234
Hope this helps!
It is difficult to test the resistance of an in-circuit resistor with accuracy, because there will almost always be alternate circuit paths. So, here's what you can do: Using any quality DMM, read the resistance of the resistor under test, and compare with the marked value, including the +/- tolerance. If you read a value that is higher than the marked value, the resistor has probably drifted up in value, particularly if it's a high value resistor. If it's open, it's bad. If you read a value lower than the marked value, then you really can't tell if the resistor is good or not, because you could be reading the resistance of the alternate circuit path. Not a lot of help, is it.
The only accurate, reliable way to test whether or not a capacitor is functioning correctly is to both measure the actual capacitance and also to apply the capacitor's stated working DC voltage and check for current leakage. Obviously, putting two test leads on the cap while it's in circuit and pumping 630 VDC into your amp isn't something that anybody will ever do. Heaven knows how many things you'd fry. So, the next best way to test an in-circuit capacitor is with an ESR (Equivalent Series Resistance) tester. These are readily available, and the prices run from quite reasonable (<$100) to a lot higher (~$1,500) for a professional quality instrument. Kits are available, as well.
There are acceptable ranges of ESR based on the capacitance and voltage value being tested, and if it's out of range then it's probably bad. However, it could still be inside the acceptable ESR rating, but show leakage when under full operating voltage. An ESR tester only applies a tiny test voltage (in the mV range) to the capacitor during the test. Edit: One other thing, it's my understanding that ESR testing is only reliable for capacitors that are larger than 1 uF (approximately).
Some interesting links:
http://octopus.freeyellow.com/esr.html
http://ludens.cl/Electron/esr/esr.html
http://www.members.shaw.ca/swstuff/esrmeter.html
http://www.electronix.com/catalog/product_info.php/cPath/17_489/products_id/18234
Hope this helps!
Last edited:
Well, the ESR meter is definitely the easiest.
But now you know why so many experienced techs will tell you: "If they're old, just replace 'em!".
But now you know why so many experienced techs will tell you: "If they're old, just replace 'em!".
I often use the electrolytic leakage test on my '50's vintage Sprague TO-4 to test and reform electrolytics in-circuit. If there's a bleeder resistor or voltage divider somewhere, it may not work though - check the schematic first.
Actually, before I do that, I use the insulation resistance test from the power cord to chassis... anything less than 500 megs means there's a leaky line-to-chassis cap or something WORSE... like a bad power transformer. When it passes, it's safe to plug in.
These instruments are at least as old as the stuff we're working on, and will likely need cap replacement themselves - but except for the Sencore meters, I don't know of a modern meter that can beat 'em.
Actually, before I do that, I use the insulation resistance test from the power cord to chassis... anything less than 500 megs means there's a leaky line-to-chassis cap or something WORSE... like a bad power transformer. When it passes, it's safe to plug in.
These instruments are at least as old as the stuff we're working on, and will likely need cap replacement themselves - but except for the Sencore meters, I don't know of a modern meter that can beat 'em.
Really? I'd be scared to death. Even if I checked the schematic, I'm not sure I'd be willing to take the risk that I'd missed something somewhere. I can see myself cranking up the voltage, and then there's that little puff of smoke from somewhere. All tubes out first? Obviously the tubes won't be conducting without power, but...
I've got a nice TO-6. I'll echo your thoughts. Great pieces of equipment!
SET12
Super Member
I bought the Blue ESR kit $79
http://www.anatekcorp.com/blueesr.htm
Heres a comparison of various ESR testers
http://www.anatekcorp.com/testequipment/esrcompar.htm
Heres when and where I used it for a project I gave some details of its construction here scroll down and you'll see it. It allowed me to find a bad cap that supplied my DAC's. The guy that designed it is a well known guru for effective cap testing. I'm very satisfied and it has a lot of support.
http://www.audiokarma.org/forums/showthread.php?t=185971&page=2
SET12
Thespeakerdude8
Super Member
Are those old heathkit/knight capacitor checkers any good? They sure look cool with their magic eye tube, and can be had rather cheap, provided you recap them and replace any OOT resistors...
imready
it's good to be the king!
They are cool unit and just show shorts or opens . Kind of fun and very collectible. I have two or three because even though I'm old they still wink at me.
dewickt
Will fix about Anything
For capacitors and inductors I use a Sencore "Z Meter" (LC53), capacitors must be out of circuit , +/- 1pf up to 200,000uf and up to 600V leakage testing that can be used to form electrolytics. The settable voltage to test at has found a lot of bad capacitors that look good at 50V but change value and have leakage at 400V where they operate. I threw out a batch of new Chinese PIO capacitors that above 200V developed leakage, the Eico amp they were in kept eating outputs with them as grid blocking caps, chenged them out to new new Nichicon F caps and never had another run away.
SET12
Super Member
:scratch2:Yeah it looks to be the same circuit but in a smaller package. I enjoyed building it. And finding the bad electrolytic in my CDP paid for itself! My system uses a lot of caps like my phono supply here with the caps being 20 yrs old but they are in very good condition. Having this meter gives me some piece of mind. :yes: :thmbsp:
SET12
gogofast
Addicted Member
thanks for all the info. they all say they're suitable for in circuit testing, but is that true? do you use yours in circuit?I bought the Blue ESR kit $79
http://www.anatekcorp.com/blueesr.htm
Heres a comparison of various ESR testers
http://www.anatekcorp.com/testequipment/esrcompar.htm
Heres when and where I used it for a project I gave some details of its construction here scroll down and you'll see it. It allowed me to find a bad cap that supplied my DAC's. The guy that designed it is a well known guru for effective cap testing. I'm very satisfied and it has a lot of support.
http://www.audiokarma.org/forums/showthread.php?t=185971&page=2
SET12
SET12
Super Member
Yes I have, The Blue uses a signal level that is <100mV so it won't forward bias diodes or transistors. Also it can go as low 1uf but it really is meant for larger caps.
And if there are paralleled caps you are going to have to disconnect because the meter is going to look for the least path of resistance and there is noway around that with any meter, its as simple as that.
So with a 100mV test signal and no forward biasing anything I find it very effective for single caps in a circuit. For pie filter networks in circuit the ESR should be very low.
Good ESR meters are expensive and this is a very good meter for the $79 kit a price break through IMO.
You could spend a lot more especially for the ones that test at working voltages and measure leakage which is better. But no where near the portability and ease of use as the Blue.
One nice thing about the Blue is the test voltage is AC so you don't have to worry about polarity.
Caps should be discharged before testing.
I never want to be without one!
SET12
And if there are paralleled caps you are going to have to disconnect because the meter is going to look for the least path of resistance and there is noway around that with any meter, its as simple as that.
So with a 100mV test signal and no forward biasing anything I find it very effective for single caps in a circuit. For pie filter networks in circuit the ESR should be very low.
Good ESR meters are expensive and this is a very good meter for the $79 kit a price break through IMO.
You could spend a lot more especially for the ones that test at working voltages and measure leakage which is better. But no where near the portability and ease of use as the Blue.
One nice thing about the Blue is the test voltage is AC so you don't have to worry about polarity.
Caps should be discharged before testing.
I never want to be without one!
SET12
Ed in Tx
Super Member
I have the older DSE ESR-Low Ohms meter, and recently bought a new Blue one too. Got the Blue from "Electronix Corp" because for $3 more it includes the clear stand. No affiliation with this company btw. Just offers a little better deal on it. Plus, the stand is handy.
For years used to rely on an old Sencor capacitor tester and had to remove the caps from the board to test. How many times did a cap read good, but really wasn't, and that problem set eluded me and maybe didn't get repaired. Then came the ESR meter! Can't do without it.
For years used to rely on an old Sencor capacitor tester and had to remove the caps from the board to test. How many times did a cap read good, but really wasn't, and that problem set eluded me and maybe didn't get repaired. Then came the ESR meter! Can't do without it.
If you're talking about an ESR meter, they don't test resistors.