Using ESR meter to find bad caps in circuit....

[jdurango]

Recapping an old Harrison console and looking for the fastest/most efficient way to find bad caps. It has about 60 caps per card, so I'd really prefer to do most of the testing in circuit, and preferable NOT under load. I've heard ESR meters can be very accurate and good for identifying leaky or malfunctioning caps. Anyone have any experience with these? Any other suggestions?

I'm currently considering an ESR Micro v4.0....seems to be a very popular one among techies/tinkerers. Thanks fellas!

 

[PRR]

> good for identifying leaky
> ESR Micro v4.0

Does not measure leakage. Anyway, for supply decoupling caps, you can't separate the various caps' *and* other parts' leakage; and supply cap leakage is not serious until it causes voltage-drop or heat.

For typical supply rails, with multiple caps parallel, you can't test ESR or value without some unsoldering.

 

[jdurango]

Does not measure leakage.

Well I more meant it can detect the symptoms of leakage, which could be high ESR.

Anyway, for supply decoupling caps, you can't separate the various caps' *and* other parts' leakage; and supply cap leakage is not serious until it causes voltage-drop or heat.

This console was relatively rare (PP1) and I'm having a hell of a time finding schematics. I plan to recap the PS to get proper supply voltages, but as far as proper voltages at specific points in the circuit, I'll mostly be flying blind, or trying to trace stuff down and make an informed guess....that's why I'm really hoping I can find a method of testing caps without a load, and preferably in circuit, if possible. [/quote]

For typical supply rails, with multiple caps parallel, you can't test ESR or value without some unsoldering.

Well, the supply rails should be good after the PS is done, I'm mainly wondering about the channel modules. I'll be sure to desoldering any in parallel. Thanks man!

 

[Matt Nolan]

Well, the supply rails should be good after the PS is done

Not necessarily if you still have leaky bypass caps within the console.

I think it was posted only a couple of days ago here in another thread: it might be quicker and less expensive to forget testing and just replace all the caps.

 

[mjrippe]

To clarify what PRR and Matt are saying, there are capacitors on the power rails of each channel called "decoupling" or "bypass" caps.  These are not the caps in the power supply itself.  They can degrade and cause all sorts of problems and it is often easier to just replace them.  You can find them by tracing where the voltages come into the channel and looking for caps from the voltage rails to ground.

 

[Gold]

I can tell you that measuring ESR will give you no indication leakage current. I just went through this.  There is a Sencore cap/inductor analyzer in the Black Market. To test leakage current you'd need something like that or set up a test jig.

See the ESR meter thread in The Chamber.

 

[Rob Flinn]

If the console is 20-30 years old IMHO you would be better off doing a wholesale swap out of the caps anyway.  If you just replace the bad ones you will probably wind up having to go through the whole console again in 6 months & then another 6 months after that.  If you do the whole lot in one go at least you can be reasonably sure you wont have to mess around with the caps again in the near future.  Also once you have done that then it's easier to fault find other problems.

 

[PRR]

> symptoms of leakage, which could be high ESR.

Two very different things.

Come to my house.

My power-line is way too long, has high ESR. When I use the toaster, the lights dim.

Part of my line is underground. In damp weather current leaks, makes warm dirt, spins the billing meter.

But these are very different causes. I could have a short leaky line (underground cloth insulation), or a long leak-free line (tall glass insulators in dry air).

It *may* be true that "both" problems get worse with age. But they are different causes and surely do not age at the same rate. It may be true that the maker tries to not get "too good" on one, since the other will limit useful life. But leakage often improves the first year. ESR is stable up till the end of life when it shoots-up.

Reading ESR says nothing about leakage. (Extreme leakage shows as heat, so you could use an IR camera, except usually it is low until just before it blows.)

When you have *multiple* caps nominally parallel, you can NOT reliably test individual ESR or leakage in-system. Say the designer wanted <1 Ohm ESR in a 2-cap array. He might pick 1 Ohm caps to get a little margin. Now after 30 years, one has drifted to 0.8 Ohms, the other has shot-up to 50 Ohms (useless). The meter will show 0.79 Ohms. Is this good? Bad? Is it two caps at 1.6r each, or one good 0.8r cap holding one end of the large PCB solid, and a useless 50r cap letting the other end of the board flap on a foot of copper trace?

Likewise if three parallel caps have leakage of 0.1mA, 0.1mA, and 10mA, the 10.2mA reading might be a clue. Except you probably have 20mA of chips in parallel with the rail-caps. The chip consumption may go down with voltage, but so does the cap leakage.

You gotta disconnect the wires. If these were soup-can caps in a welding supply, you might test each one, to save as many as possible. If these are 40-cent caps in Fine Audio, where the designer assumed EVERY cap would nail-solid its local area, and you already un-soldered for test, then it may be best to just replace.

 

[jdurango]

> symptoms of leakage, which could be high ESR.

Two very different things.

Come to my house.

My power-line is way too long, has high ESR. When I use the toaster, the lights dim.

Part of my line is underground. In damp weather current leaks, makes warm dirt, spins the billing meter.

But these are very different causes. I could have a short leaky line (underground cloth insulation), or a long leak-free line (tall glass insulators in dry air).

It *may* be true that "both" problems get worse with age. But they are different causes and surely do not age at the same rate. It may be true that the maker tries to not get "too good" on one, since the other will limit useful life. But leakage often improves the first year. ESR is stable up till the end of life when it shoots-up.

Reading ESR says nothing about leakage. (Extreme leakage shows as heat, so you could use an IR camera, except usually it is low until just before it blows.)

When you have *multiple* caps nominally parallel, you can NOT reliably test individual ESR or leakage in-system. Say the designer wanted <1 Ohm ESR in a 2-cap array. He might pick 1 Ohm caps to get a little margin. Now after 30 years, one has drifted to 0.8 Ohms, the other has shot-up to 50 Ohms (useless). The meter will show 0.79 Ohms. Is this good? Bad? Is it two caps at 1.6r each, or one good 0.8r cap holding one end of the large PCB solid, and a useless 50r cap letting the other end of the board flap on a foot of copper trace?

Likewise if three parallel caps have leakage of 0.1mA, 0.1mA, and 10mA, the 10.2mA reading might be a clue. Except you probably have 20mA of chips in parallel with the rail-caps. The chip consumption may go down with voltage, but so does the cap leakage.

You gotta disconnect the wires. If these were soup-can caps in a welding supply, you might test each one, to save as many as possible. If these are 40-cent caps in Fine Audio, where the designer assumed EVERY cap would nail-solid its local area, and you already un-soldered for test, then it may be best to just replace.

Okay, think I got it. As you can probably tell I'm relatively new to this stuff. I've got a couple very trusted techs telling me "why the hell would you waste time and money repacling perfectly good caps?" but a lot of very respected people on these forums telling me to just recap the whole thing. I'm leaning towards the latter.

It's a lot easier for a pro tech to "simply" find the bad caps and replace them....and then do it again a few months later...and perform all the necessary measurements and audio tests to confirm everything is working properly. But I'm a musician/producer first and foremost and a gear head second. I like this stuff, but I'd rather spend my time making MUSIC! Anyhow, thanks very much for the help!!

 

[pucho812]

caps are pretty inexpensive in comparison to other parts so the cost of replacing one vs replacing 5 or what have you is pretty  negligible. The time however doing it is not.  If it were me, I would do the whole lot based on age.... 

 

[Gold]

When I was asking I was seeing if I could avoiding replacing big can PSU filter caps that are in unique mounts. They need an exact replacement in the same form factor. One cap in the form factor i need is $42.50 at mouser. I need eight. There are a dozen others that are about $10.00 each.