Ray,

                    Rather than smoking the part, why not put a current meter, with a range of 500 mA in series between the Power Supply, and the part. Use a variable Power Supply with a calibrated voltage meter, there should only be current for a moment when raising the voltage on the power supply to the part's rated voltage, which would be the charge current.  The faster the voltage is raised, the larger this current will be, and the faster the current will fall to 0.  Once the cap is charged (quick), the current should drop to 0, if it does not, then the cap has a problem, either mislabeling, misstated Working Voltage, or a resistive cap.  This would be a great way to prescreen these problem parts, before making the investment of inserting it into the PC Board, saving rework time later on. Once the weeding process stops or significantly slows in finding bad parts, the pre test could then be abandoned.


Ron Leckfor, BSAS-EET
REM Electronics Supply
Value Added Division
Quality Control Coordinator


-----Original Message-----
From:   Raymond Klein [SMTP:[log in to unmask]]
Sent:   Thursday, June 03, 1999 3:45 PM
To:     [log in to unmask]
Subject:        Re: [TN] Tantalum caps and the big bang

Ron,

In the past 20 or so years I've seen about 6 lots of tant caps the were
polarity mis-labeled. They get quite hot and pop. One even smoked a trace
on the PWB. (My fault for making it too thin).

You can test caps by putting them directly across a DC supply at 1/2 the
rated voltage. The supply should be able to supply at least 1 amp. If the
cap gets hot in a few seconds its "+" lead (what ever its marking) is
connected to the "-" lead of the power supply. Wear safety goggles as com
caps can fail spectacularly. Also be careful touching them as they can
raise a blister.

Good luck - Ray Klein

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