[sdiy] finding bad caps

[Travis Shire]

> Curious if any of you guys have suggestions on capacitor testing
> instruments.
> I have used the BK 875A LCR meter, an ESR meter, and a Huntron and am 
> really
> not satisfied that I can use these to find bad electrolytic (or other) 
> caps.
> Right now I am just going through some non-working things in my garage, 
> like
> motherboards and LCD monitors.  I see obviously bad electrolytics pull 
> them,
>
> replace them, and many of these things then worked.  But I take those same
> parts and put them on the various instruments and not much becomes 
> apparent.
> Frustrated, I do some research.  There are a couple "cap analyzer" 
> products
> out there - but I'm thinking they work like my ESR meter.  The ESR meter
> does show some variance, but isn't good enough to find everything.  I then
> read about Sencore cap analyzers...  there have been many different models
> over the years.  They test caps 4 different ways. Seem like maybe they 
> would
> be the best bet as they test at rated voltage for dielectric absorbtion 
> and
> leakage as well as capacitance and esr.  There are so many different 
> models
> I ask if you may know if it makes much difference or even if these have
> proven worthwhile units to have for you.  I have ordered a demo of the 
> cream
> of the crop LC03 for a work-related demo to see if it can determine 
> anything
> worthwhile about MLCC caps - the guys at Sencore didn't really know how
> weird MLCC's can be with DC bias... and had not tested them with the LC03.
> After looking at that I'll look at those bad electrolytics...  but I will
> never spend that kind of money on a cap tester for home...  Maybe you know
> of some old jewel tester with the tuning eye tube that does what I want?
> There is a youtube video of a guy recommending one of these but ebay and
> craigslist come up empty finding one.
> I know many of you just guess the date of caps and replace the older ones
> but I'd really like to nail this if I can.
>
> Barry


I use a Sencore LC77 in my shop. Actually I have 2, but one quit recognizing 
the presence of the leads a while back so I called in the backup. They are 
handy to have, but not essential. I'll use mine quite a bit to check the 
condition of older lytics that may be questionable. If they show above 
average leakage current I replace them. Just because they are working now 
don't mean they will be a few months from now. Caps are cheap compared to 
bench time and my customers appreciate the heads up and will normally opt 
for the cheap insurance policy of fresh caps.

They are also nice if you buy from surplus vendors. I tend to use high 
voltage lytics from surplus guys for my own projects and anything that comes 
from them is put on the 77 to check condition before it goes in the circuit. 
I've had great luck so far, only a couple duds out of a hundred or so parts. 
I've also identified counterfeit caps with it as well.

Wind coils? It checks the inductance value. Bought a box of film caps at a 
ham swap and want to check them before use? Great for that.

So if you can justify shelling out the dough for one, they're nice to have 
around. Most consumer elect techs will just check for value and ESR in 
circuit and replace anything that reads funny. These days with consumer 
stuff, most failures can be traced back to poor quality caps.....

You should be able to find a LC77 or 102 on ebay fairly reasonable. Still 
not "cheap", but even those old Sprague "tel-ohmike" jobs are getting 
popular with collectors....so they're not cheap either.