First, the TS writes there is no other way to find bad caps. That is not true. If you know what you are doing you do not need an ESR meter. It is a handy replacement for knowledge. Most times you replace more caps as needed but that is often not bad. In consumer stuff, if a few caps fail, the rest will follow. Just replace them all at once instead of a few every now and then.
I repair a lot, but most of it is test gear, not much consumer electronics, and I never measure ESR in situ. I find most problems using a scope and multimeters. And if it does not run, I desolder the caps, reform them, test for leakage, capacitance , D and ESR. If it can be powered I use a scope and if find a problem regarding caps, I desolder it and then I start measuring it but that is because I like to study component behauvior and then want to know what en why it fails. (I have a lot of capacitance/impedance/ESR etc mearsurment gear)
I think both partys are right. ESR is meaningless and ESR is important. Depents on your point of view.
Electrician is right, ESR can be an important parameter in design. In a lot of cases it must be low to minimise dissipation. Sometimes it must be high to keep something from oscillating. So if you repair a circuit, it can be important to use a cap with the right ESR. And that means, the same ESR. Low ESR is not defined. If I make caps and my best one is 1000 Ohm, then I am allowed to call it a low ESR cap. While an other brand can makes a cap with 0.000001 Ohm ESR, so his 0.01 Ohm version is his high ESR cap.
But in case you measure ESR need to know the specs to make a judgement, or have enough knowledge to know what would be right. Most 1uF caps are sloughtered after false accuse with an ESR meter. My IET and my homemade ESR meter measure 1 u with out problems. My homemade down too 100 nF and less accurate even lower. The IET DE-5000 measures everything you feed it. Most of my bridges do too.
ESR as a value while searcing for faults in a circuit is a bit meaningless. OK, it can be handy as a replacement for knowledge about fault finding. But it is meaningless because you must know the ESR. And most users only use some table on the meter. But who cares. If it is 1 to 5 years old an caps fail, replace them all or junk it.
And that is the funny part. Most ESR meters measure impedance at 100 kHz and do not measure ESR.
The datasheet often states the impedance at 100 kHz. That is not the same as ESR. ESR is a part of impedance.
The datasheet states D, sometimes also ESR as it is related to D, but at 100, 120 or 1000 Hz, not at 100 kHz.
So real ESR meters that measure at 100 kHz give you real ESR but that is a number that most times can not be verified for 100 kHz. And the not-ESR meters that measure impedance , that is in the datasheet at 100 kHz, tell you they measure ESR instead of impedance.
I agree with the people here, that do prefere D (dissipation factor or DF, if you know it, it's a very logical parameter. )over ESR. I do too. I have several ESR meters, have a collection of bad documenteed caps and a whole bunch of bridges and analysers for caps but I use D.
There are a few failure modes:
- low capacitance
- DC leakage
- high D (and ESR)
- mecanical failures
These things can be on their own or combined.
There is one pitfall, many people who repair consumer stuff measure capacitance with a multimeter that uses DC. If ESR gets up, and if capacitance decreases also, the meter is fooled by the ESR and gives a capacitance that can be the double of what it is. The same is true for not vectorial impedance meters.
I have seen caps that failed in one of the modes above and caps that have more of the problems.
I have seen caps with a great ESR. But totally shorted for a few volts DC. The ESR meter will not find it. The capacitance meter with an in circuit usable signal amplitude will not alway find it. capacitance can be good. Only a leak test will find it. And often a good bridge will too because they some can generate a rather high voltage.
I have seen high ESR and good capacitance and no leakage. A high voltage cap had good ers and good capacitance but it looked like a geiser in circuit (blowing a lot of smoke ) It did not leak DC far below the working voltage but around 10V below the working voltage in circuit, it started leaking severe, You would not have find it if you had not seen it blow smoke and only used ESR OR lcr meter.
That is why I think only measuring ESR in situ is a bit meaningless.
http://www.pa4tim.nl/?p=3775 my page about the ins and outs of ESR measurement.
And about 1000 other topics here about ESR