Testing capacitors for damage.

Muaguana · #1 09-10-2010, 12:45 AM

I've been doing a lot of soldering lately with capacitors - trying treble bleed circuits - and I was wondering it there was a way to determine whether or not a capacitor has been damaged by excessive heat (enough to affect its performance, that is) without plugging the bass in. Basically, I'd like to make sure I didn't cook the dielectric material immediately after attaching it to a pot instead of having to reassemble the control cavity to find out. I also have a bunch of capacitors that I've used and removed and would like to make sure they're in working condition before using them again (I'm not exactly the most gentle de-solderer on the planet...)

First off, if a capacitor's dielectric material is damaged from heat, will its capacitance change or will it cease to pass signal from one lead to another altogether? Bearing that in mind, will the capacitor show signs of physical damage (i.e., the insulating material melting) before the dielectric material is compromised? Or is there a way to test with a multimeter? I'm thinking that if the capacitance had changed, I would need to find the resistance between the leads and then use some formula (either Figure or Merit or Reactance?) to find the capacitance. Would that work, or am I completely off?

DUC1098 · #2 09-10-2010, 12:55 AM

They do make capacitance meters. I have never run into a capacitor damaged by soldering, etc. If you cooked a cap, it will usually explode (which really stinks, quite literally) or swell up (pre-explosion). I would think that a cap would either pass no current or act as a short should the dielectric be compromised.

I am a degreed electrical tech, but haven't used it in several years, so I am a little fuzzy on component "specifics".

xaxxat · #3 09-10-2010, 09:14 AM

You'll need a capacitance meter to check a cap.

**line6man** · #4 09-10-2010, 10:17 AM

Yep, a capacitance meter is all you need.

While you're at it, check the tolerances on your caps and pick the good ones to use in your bass.

okcrum · #5 09-10-2010, 10:58 AM

You'd pretty much have to set fire to a non-electrolytic cap like a bass' tone cap to damage it. I've seen caps with the ends melted or burned from poor soldering that worked just fine. That's not to say they never fail; it's just that modern ones tend to fail all the way or not at all. Now, if you're talking paper capacitors, they can get leaky over time. A capacitance meter, or a multimeter that measures capacitance (most decent ones do, even from Radio Shack) will tell you about problems straight away.

**line6man** · #6 09-10-2010, 11:18 AM

Quote:

Originally Posted by okcrum

You'd pretty much have to set fire to a non-electrolytic cap like a bass' tone cap to damage it. I've seen caps with the ends melted or burned from poor soldering that worked just fine.

I agree with this.

It does take a lot of heat to damage many capacitors.

Something you might want to look into if you are worried though, is the use of a clip-on heatsink when you solder the caps.

It's basically an aluminum clamp/pair of tweezers sort of thing that you clip onto components like TO-220 cases when you solder them in order to dissipate the heat and avoid damage.

It would probably help to dissipate the heat from soldering if you clipped it onto the capacitor leads.

Muaguana · #7 09-10-2010, 07:07 PM

I searched for capacitance meters a while back (since my multi doesn't have that capability) but they're a wee bit outside my budget range at this point. Probably my only option, though, if I get paranoid enough to want to check that value.

Quote:

Something you might want to look into if you are worried though, is the use of a clip-on heatsink when you solder the caps.

That's the one thing I keep forgetting whenever shopping online or at Radioshack. I use hemostats at the moment, but their size and weight often makes working with small components a PITA.

Thanks for the insight, guys. One more question (I can't believe I'm going to ask this, but I just want to make sure): when soldering a capacitor and a resistor in parallel between two pot lugs, is there any difference between these two diagrams, in terms how the capacitor and resistor affect the electrical signal?

A.

i.e.,

(Line6man I am not)

B.

i.e. ... ?

Probably a stupid question, and I'm 90% sure of the answer, but for some reason the two leads being connected at the same point throws me off.

**line6man** · #8 09-11-2010, 11:08 AM

Quote:

Originally Posted by Muaguana

I searched for capacitance meters a while back (since my multi doesn't have that capability) but they're a wee bit outside my budget range at this point. Probably my only option, though, if I get paranoid enough to want to check that value.

That's the one thing I keep forgetting whenever shopping online or at Radioshack. I use hemostats at the moment, but their size and weight often makes working with small components a PITA.

Thanks for the insight, guys. One more question (I can't believe I'm going to ask this, but I just want to make sure): when soldering a capacitor and a resistor in parallel between two pot lugs, is there any difference between these two diagrams, in terms how the capacitor and resistor affect the electrical signal?

A.

i.e.,

(Line6man I am not)

B.

i.e. ... ?

Probably a stupid question, and I'm 90% sure of the answer, but for some reason the two leads being connected at the same point throws me off.

A and B look exactly the same to me. I don't see any differences.

Or unless you meant A and B compared with the schematic drawing?

xaxxat · #9 09-11-2010, 12:14 PM

Quote:

Originally Posted by Muaguana

I searched for capacitance meters a while back (since my multi doesn't have that capability) but they're a wee bit outside my budget range at this point. Probably my only option, though, if I get paranoid enough to want to check that value.

Look on Ebay for an LCR meter. I've seen some go for less than $20.

**line6man** · #10 09-11-2010, 12:20 PM

Quote:

Originally Posted by xaxxat

Look on Ebay for an LCR meter. I've seen some go for less than $20.

Yep.

I almost bought a cheap ammeter clamp/multimeter once, but I figured it was probably a piece of crap.

The seller had hundreds of them for something like $10 Buy It Now.

warnergt · #11 09-11-2010, 12:25 PM

$30.88 new
http://cgi.ebay.com/20mF-200mF-Capac...item255ca752d1

Muaguana · #12 09-11-2010, 09:15 PM

Quote:

Originally Posted by line6man

A and B look exactly the same to me. I don't see any differences.

Ok, cool, just double-checking (read: making sure I wasn't going crazy or something.)

Thanks to everyone for the tips on the capacitance meters, too; I'll check them out.

fdeck · #13 09-11-2010, 09:59 PM

I'm thinking that you can buy a bag of new capacitors for the price of a cap meter.