Yes, it is possible for the plates to realign. It is still cracked, the part
is damaged and should be replaced. Heating the part may remove the symptom
but it is not a repair.

There are, very likely, other parts that are damaged. Most capacitors are
by-pass filters across the power supply. Often as not, you could even remove
one or more of them and the circuit will continue to function normally.
The situation you describe can easily result in an increase in current from
the power supply. A battery operated circuit would drain the battery more
quickly, even though it might function normally.

Here is the dirty laundry, this happened a few years ago when I worked for
an OEM:
Field returns for slow clocks. The clock was part of a memory, circuit, like
ones common on computers. The battery supplied power to keep the CMOS memory
refreshed and ran the real time clock. We discovered, after many engineering
fixes, set-up procedures, product tests. That, the boards returning from our
customers with clock problems had a cracked ceramic capacitor.

Here is what the day was like:
I discovered high current draw on a field return board. Removed all the caps
until the current draw returned to normal.
I measured the cap, it was normal.
I measured across the pads (battery out of circuit). OPEN.
Installed the cap. measured 10K ohms across the cap.
Removed the cap. measured open.
Installed the cap. measured 2K ohms.
Got a different meter, and another Engineer, as I needed moral support.
Measured the cap 560 ohms.
Removed the cap. measured 100K ohms.
Made a collection of all the boards that had drained batteries. We had five
or six in the warranty return bin.
Removed the cap in question from all the retunes. All had some resistive
component.
Sent them to AVX for evaluation. They returned beautiful glossy prints of
cracked capacitors. Conjecture, mechanical damage, based on the nature of
the cracks. We made adjustments to placement programs, source controls (so
all parts with a given part number were not only the same value, voltage and
tolerance but also the same thickness), and improved machine maintenance.
Problem solved. In addition, we stopped getting returns from customers that
did not care about the clock but had trouble with CMOS memory failures.
I wonder how many power supplies were damaged by excess current draw. We had
recently redesigned one supply so it could deliver 20 amps at 5 volts when
12 should have been enough.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ahmet Coþan
Sent: Friday, April 21, 2006 7:22 AM
To: [log in to unmask]
Subject: Re: [TN] Capacitor Metamorphosis


Dear Mr. Ramsey,

thanks a lot for your fast response,

However, i want to emphasize that after heating up the capacitor with
soldering iron for 5 seconds, we don't see a resistive behaivour any longer
in our capacitor. Does a cracked cap can be repaired after a similar
heating process?

Thanks for your help again.

Best regards,

Ahmet

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