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Cap Checker

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Posted on July 5, 2018 at 00:07:08
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 We all know the caps can affect the sound. How much may be in contention but that is beyond the scope of this text. Some restore audio, modify audio by putting supposedly better caps and even resistors in. Fine and dandy, but some times, even in mid fi, something goes wrong and it is obvious to your old Aunt Matilda who has been nearly deaf for a decade. Noticeable distortion in a channel or lower volume. Many times this it because of bad caps.

This is not a matter of getting out the old 339a and the spectrum analyzer, it is a matter of finding out if the caps are capping. So
I designed a cap checker about 3 decades ago and lost the whole damn notebook on it. I did it again but never got it to where I wanted it, but with LTSpice I think I am getting there.

The picture will show up, but having the file is better. It is at :

https://groups.google.com/forum/?hl=en#!topic/sci.electronics.basics/Nli1uFN1Tu8

The second post. And there will no doubt be some discussion there.

But here is a picture of the schematic so you can at least see it. I will be back with explanations on how each section works and of course it is not done. Any engineers, speak up. Some things are not quite figured out yet, the oscillator, that is not a major problem, and the ESR detection diodes have has a mod, adding two forward biased diodes to ground for the "bottom" diode of the voltage detector. This eliminates their Vf.

 

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RE: Cap Checker, posted on July 5, 2018 at 00:08:44
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016



No pic, shoot the, umm I don't know who just shoot someone OK ?

 

RE: Cap Checker, posted on July 5, 2018 at 00:10:28
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 I will be back with the circuit description etc.l so it can be discussed.

 

RE: Cap Checker, posted on July 5, 2018 at 00:42:27
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 For one, I know the oscillator won't work. That is not hard to fix.

As far as that link to Usenet goes, read all of it if you want. If this ever flies I might not be able to patent it but I can certainly prevent anyone else from it. Prior art, and nothing is ever deleted on Usenet.

 

RE: Cap Checker, posted on July 7, 2018 at 12:40:06
Cleantimestream
Audiophile

Posts: 7551
Location: Kentucky
Joined: June 30, 2005
 Perhaps your propeller spins faster than others here and your flying above them, Chief?
The Mind has No Firewall~ U.S. Army War College.

 

RE: Cap Checker, posted on July 7, 2018 at 14:04:33
Mike B.
Audiophile

Posts: 26356
Location: OR
Joined: September 27, 1999
Contributor
  Since: September 1, 1999
 I can appreciate what you are trying to create but don't have the skills to help. We had a number of EE's here when the place started, but the ones I remember have moved on. DIY Audio has a number of them. Threads there can get frustrating taking off in a number of side journeys. The problem with sharing intellectual property is you are open to have it stolen and it could be by someone located where all the rules are out the window on copyrights. Good luck with this idea.



 

RE: Cap Checker, posted on July 8, 2018 at 19:48:07
AbeCollins
Audiophile

Posts: 46306
Location: USA
Joined: June 22, 2001
Contributor
  Since: February 2, 2002
 So what parameters of a capacitor are you trying to test for? And ... "it is a matter of finding out if the caps are capping." doesn't cut it ;-)

There are several inexpensive LCR meters on the market as well as much more expensive units that cover a broader impedance, frequency, and voltage range, along with much greater accuracy.

The Keysight (Agilent) E4980A Precision LCR Meter, 20 Hz to 2 MHz is $18,000 USD but you can find hobby grade LCR meter capability built into many cheap DMMs.

There's a dedicated capacitor ESR tester for $100 linked below. In the body of the webpage linked below you will see another link for "Comparison of some ESR meters" with a few more relatively inexpensive capacitor ESR meters.

So what does your capacitor tester do that the others on the market can't do?



 

RE: Cap Checker, posted on July 9, 2018 at 23:13:06
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 "So what does your capacitor tester do that the others on the market can't do?"

It beats their speed and ability to read fast.

 

RE: Cap Checker, posted on July 14, 2018 at 13:29:33
Coner
Audiophile

Posts: 3703
Location: S.W. Washington state, USA
Joined: November 17, 2001
 Yes, the Dayton DATS unit checks ESR at 3 different frequencies and
close to instant results..1 sec. or less. Proved to be very accurate
comparing to my Fluke meters. Cheap too.

 

RE: Cap Checker, posted on July 14, 2018 at 18:26:56
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 Mine reads in quite a bit less than a second. And it measures pretty much all frequencies above 5 KHz.

A Usenetter said using 1 KHz brings in too much Xc to read ESR right, but he apparently didn't notice the high pass filter going to the buffer for the actual detector.

He is one of them guys who thinks he knows everything and turns to personal attacks when proven wrong. However he is quite competent. He just missed that. After his oh so polite response I decided not to respond and enlighten him to the high pass filter. Let him stand in error.

However there is a possibility that I will raise the frequency of the high pass filter to further take Xc out of the measurement. I thought I would at least breadboard it first though.

If you want to join groups.io there is a detailed writeup on a cap checker that uses only a generator and a scope. This is my idea though like many I found that someone else also did it. Like the DBT, I really did invent it but so did tons of other people. I was not even a teenager at the time. The house had fuses and one kept blowing, we would unplug a few things and replace the fuse and it would blow again. So instead of buying more fuses I put a lightbulb in for the fuse and started disconnecting things until the light went out.

Anyway, that cap checker with the scope, you look for the part of the square wave that is across the cap and the part where the trace is almost invisible because of the slew rate exceeding the writing speed of the scope, that represents the ESR. You could actually look at that part of the waveform and see the amplitude of that portion and read the voltage, do the math with the original 400 mV and derive the ESR by simple ohm's law. But for servicing we didn't bother, the idea was a go/nogo test. The scope I installed it in developed a fault and they begged me to fix it or build them another one, and this is after I quit working there.

So that's why I only want to detect the higher harmonics of the square wave, it is a more useful indication. On a bit higher value caps you saw a triangle wave, you look for the break between the top and bottom parts of it. Even higher value caps ESR would result in a square wave, perfect would be a flat line. Lower value caps you was like a quarter sine wave, but still there was a part that was straight vertical and due to the slew rate the trace was much darker. That's the ESR.

If I had used 100 ohms as a source impedance the math would have been easier if you wanted to actually know the ESR. But lower value caps would be harder to read. We wanted to be able to read it at some distance, and I put like 6 foot probes on it. And this is a Tek 7613 on a scopemobile, so everybody could use it, once I taught them how. But sometimes it was hard to get it close. This method provided the most readable display under the circumstances.

Speaking of readability, if this takes off I am not having it like many DVMs that either lay down or you lean them on something. It will be setup so it is easy to see, maybe a 45 degree angle, and NOTHING reflective on the front. All matte finish, no glare. that has always been a terrible problem in servicing, at least how I did it. And the stand is not going to be a glorified coat hanger. And I want the surrounding of the display blacked out. I want it so you can read it in direct sunlight without using a friggin 18 volt battery pack to light the LEDs. And I refuse to use an LCD.

I've made a couple of mods since I posted that schematic. I might post them soon if there is any continued interest.

 

RE: Cap Checker, posted on July 15, 2018 at 11:10:57
Coner
Audiophile

Posts: 3703
Location: S.W. Washington state, USA
Joined: November 17, 2001
 Thanks...I respect what you're doing and knowledge, but in my
applications, I don't need anything exotic. I don't deal with
any audiophiles really, just the average joe that wants their
speaker fixed an/or re-capped, but I find capacitors facinating
with all the different types and materials used.

 

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