Capacitor... What Did I do Wrong?

[illucius]

So, I have a PCB with a cap in it and wanted to monitor the voltage level of it. I hooked up an oscilloscope to it and then heard a pop. I think the cap popped. What did I do wrong here? Am I not supposed to hook a cap to an oscilloscope and is it possible to verify if the cap is what caused the pop?

 

[yoramgr]

Scope is not like a floating battery operated voltage meter (unless is is a battery operated scope...)
and, if your PCB is powered from a power supply connected to the mains, most likely the PCB and the scope share the same GND (through the ground pin of the mains socket).
This GND is the scope's probe GND. When you connect the GND side of the probe to one side of the CAP, and this side of the CAP is not at GND potential, this could be a problem...
Either you shorted some voltage to GND, causing a problem somewhere in the PCB or the power supply, or it increased the voltage over the CAP above it's maximum rating.

To measure the voltage across the CAP (or across other element), connect the GND side of the probe to GND of the PCB, and take two measurements, from the two sides of the CAP, and subtract (or use two probes and use the scope subtraction function).

 

[siles]

Reverse polarity will pop capacitor .use multimeter to measure ac/dc level.

 

[KJ6EAD]

If it's an aluminum can electrolytic capacitor, you may see the case bulged out at one end after catastrophic failure.

 

[illucius]

Hmmm... I'm pretty sure I didn't reverse the polarity of the cap. Is there any other way I could have caused damage to it?

Also, is it possible to check whether the cap is working or not using a multimeter or anything without having to pop it off the board?

 

[yoramgr]

Any chance you could post the schema and point out which capacitor is it?

 

[agorts]

...........

 

[mrjava241]

What's the spacing between the cap you probed and neighboring vias/pins/pads? Any chance that you could have momentarily shorted something?