Burned capacitor

slowpogo · 4th April 2007, 11:08 PM

I was soldering an adjacent resistor onto a PCB, and bumped a Wima box cap with the iron. An area about 1 or 2 mm in diameter of the surface material layer, maybe .5 mm thick whatever it is, was melted away, revealing another material (also reddish) beneath.

The project isn't finished so I can't test it out. Is this damage cosmetic or will it impair the functioning of the cap?

Boris_The_Blade · 4th April 2007, 11:17 PM

To be safe, discharge the cap through a resistor if it wasn't fully discharged with the pop (being careful not to shock yourself if it is high voltage). Then take a meter and measure the resistance across the leads. If it is working correctly, it should start at a low resistance and then climb to infinity. This will happen at a speed depending on the cap size.

slowpogo · 6th April 2007, 02:30 AM

The caps (on a Tangent crossfeed board) have never held a charge, so no discharging necessary...but I did try testing them as you said, and can't get any kind of reading out of any of them, not just the "damaged" one. The caps on my PIMETA board do exactly as you say...but doing the exact same thing with the crossfeed caps, clipping onto the leads with my meter (still soldered in) produces nothing.

I did try resituating the alligator clips several times, and can't even get an intermittent reading.

Conrad Hoffman · 6th April 2007, 04:24 AM

The most common failure mode would be a short if you melted the layers. Just guessing, the inner reddish material is epoxy, and the outer box is some common plastic. I doubt you did any damage unless you melted right into the inner layer. Small value caps will just look open- you'll never see them charge or discharge on a meter because it happens too fast. If it isn't shorted, and you can pass a signal through it, I wouldn't worry. If you want to wreck something fragile, touch a soldering iron to a tubular polystyrene- instant destruction. Or, hit it with flux solvent- dissipation degradation. By comparison, box caps are pretty tough.

slowpogo · 6th April 2007, 04:29 AM

OK, the cap in question is .022uf, while the other ones that tested out were 6.8uf and greater, so that makes sense. Thanks!

4th April 2007, 11:08 PM	#1
slowpogo diyAudio Member Join Date: Jan 2007	Burned capacitor I was soldering an adjacent resistor onto a PCB, and bumped a Wima box cap with the iron. An area about 1 or 2 mm in diameter of the surface material layer, maybe .5 mm thick whatever it is, was melted away, revealing another material (also reddish) beneath. The project isn't finished so I can't test it out. Is this damage cosmetic or will it impair the functioning of the cap?

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4th April 2007, 11:17 PM	#2
Boris_The_Blade diyAudio Member Join Date: Mar 2007	To be safe, discharge the cap through a resistor if it wasn't fully discharged with the pop (being careful not to shock yourself if it is high voltage). Then take a meter and measure the resistance across the leads. If it is working correctly, it should start at a low resistance and then climb to infinity. This will happen at a speed depending on the cap size.

6th April 2007, 02:30 AM	#3
slowpogo diyAudio Member Join Date: Jan 2007	The caps (on a Tangent crossfeed board) have never held a charge, so no discharging necessary...but I did try testing them as you said, and can't get any kind of reading out of any of them, not just the "damaged" one. The caps on my PIMETA board do exactly as you say...but doing the exact same thing with the crossfeed caps, clipping onto the leads with my meter (still soldered in) produces nothing. I did try resituating the alligator clips several times, and can't even get an intermittent reading.

6th April 2007, 04:24 AM	#4
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	The most common failure mode would be a short if you melted the layers. Just guessing, the inner reddish material is epoxy, and the outer box is some common plastic. I doubt you did any damage unless you melted right into the inner layer. Small value caps will just look open- you'll never see them charge or discharge on a meter because it happens too fast. If it isn't shorted, and you can pass a signal through it, I wouldn't worry. If you want to wreck something fragile, touch a soldering iron to a tubular polystyrene- instant destruction. Or, hit it with flux solvent- dissipation degradation. By comparison, box caps are pretty tough.

6th April 2007, 04:29 AM	#5
slowpogo diyAudio Member Join Date: Jan 2007	OK, the cap in question is .022uf, while the other ones that tested out were 6.8uf and greater, so that makes sense. Thanks!

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