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Detecting reverse polarized capacitors in circuit before they explode?

Latch
I need a way to detect if capacitors are installed backwards (reverse polarized) in a assembled PCB. There are some automatic test equipment (ATE) that can handle the job, but they are more elaborate and expensive than I am willing to pay.
A small circuit to detect the issue is all I need.
 
I suppose the best defense is better QA/QC, but what are your ideas?
 
Latch
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  • The Mk1 eyeball and an ammeter seem to be a very good way of spotting these, the creeping up of the supply current even when it's in a steady state. during the time I spend testing PSU's this saved many bangs. Even feeling the drag of the variac was a giveaway.

     

    One other way is a design easthetics one, if all the electrolytics point in the same direction then it is much easier for any wrongly inserted ones to be spotted.

     

    It may be possible to tweak the ATE (assembled board, non functional) settings by applying a bias, but it's not likely to work if it's one across a supply rail as the characteristics of the rest would make it unlikely for you to be able to set the limits fine enough to detect the difference.

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  • The Mk1 eyeball and an ammeter seem to be a very good way of spotting these, the creeping up of the supply current even when it's in a steady state. during the time I spend testing PSU's this saved many bangs. Even feeling the drag of the variac was a giveaway.

     

    One other way is a design easthetics one, if all the electrolytics point in the same direction then it is much easier for any wrongly inserted ones to be spotted.

     

    It may be possible to tweak the ATE (assembled board, non functional) settings by applying a bias, but it's not likely to work if it's one across a supply rail as the characteristics of the rest would make it unlikely for you to be able to set the limits fine enough to detect the difference.

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