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I repair intelligent lighting fixtures. These devices have a large number of motors, and so they also have a large number of motor drivers. It's not uncommon to have a single PCB with more than a dozen individual motor drivers mounted. A common issue with a particular series of fixtures is a driver failing in such a way that the 24V motor supply rail is shorted to ground. (Here's the datasheet for the driver in question)

My question: How can I identify which driver has failed, without desoldering multiple drivers until the short goes away?

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Put 2A, maybe 3A on the rail and carefully touch them one by one. The failed will be hot.

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  • \$\begingroup\$ I had considered this and tossed it aside, but I guess I wasn't thinking about my benchtop power supply. Looks like there might be two shorted. Thanks for the input! \$\endgroup\$ – Derek Jun 5 '15 at 16:59
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In general, the old practical (but no as "pretty" as desoldering one by one) method to find a short inside one of a bunch of ICs with common supply is to burn it! It's not a joke - simply you need a laboratory power supply with proper voltage (24V in that case) and a few amps current capability with regulation. Connect power supply to 24V rail, set 24V voltage as maximum and slowly increase current from 0 to the moment when You can see a smoke or other interesting heat-related phenomenon on one of the ICs and, voilà, this is the bad one. Sometimes it is enough to pass a few miliamps and the bad one should be hot, test it with finger (don't do this at home!) or infrared thermometer.

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