Hi all,
We're in the process of building a run of boards. This is a microcontroller-based timer. One of the components on the board is a small, through-hole electrolytic capacitor (100uF, 16WV).
Well, after we'd built 100+ boards, I noticed that one of the caps in the bag had ITS NEGATIVE POLARITY BAND ON THE BODY POINTING AT THE LONG (+) LEAD!! The shrinkwrap was 180 degrees out of place (and no, it's not loose -- it was installed wrong at the factory)!
These capacitors are from an authorized distributor, and are made by a very well-known and ostensibly reputable manufacturer. I won't mention the maker, since the intent is not to bash a particular company. I have contacted the manufacturer and they told me to stop using the lot of parts.
However, we now need a simple way to test the capacitors that have already been installed on the boards. Obviously, we cannot check visually, since the "-" band may actually point toward the "+" lead. The leads have been trimmed, so we cannot judge by lead length. These caps have isolated metal cans; the can is NOT connected to either lead, so a continuity test from can to leads is out. There are NO vent lines on the top of the can, nor are there any other visual marks besides the suspect band on the can's shrinkwrap.
Reworking all of the boards is NOT an option, due to a tight deadline. We can replace SOME of the caps if they are definitely reversed.
I have seen some studies that indicate that reverse polarity, if the cap is operated well under its max. WV, is tolerable. However, if the capacitance of the part decreases significantly because of damaged electrolyte, it is likely that our circuit will malfunction (due to power dips caused by the relay engaging).
So, in summary, this post is:
1.) to vent (no pun intended) about crappy QC and the time it costs us engineers
and
2.) to ask for a test method to check in-circuit. Simpler is better, since it may not be an EE conducting the test.