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I burned a circuit by applying reversed polarity voltage. I measured the LDO that is supplied with 5 V and should output 3.3 V, however it only outputs ~2 V.

Now what can I deduce from that? I would expect the semiconductor LDO to not output anything after being burned, however it does. Could this mean that some of the auxiliary components (capacitors) are blown?

LDO in question is a XC6201P332 (datasheet)

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I measured the LDO that is supplied with 5V and should output 3.3V, however it only outputs ~2V.

I have seen voltage regulators which produced a different (out-of-specification) voltage, after a reverse voltage input. Therefore based on experience, your ~2 V output could mean that the regulator has been damaged.

I would expect the Semiconductor LDO to not output anything after being burned

Electronics does not always "completely fail"; there are many partial failures which can also occur. Therefore I would not expect the same as you.

Could this mean that some of the auxiliary components (capacitors) are blown?

Capacitor damage is also possible, especially if there were any polarised capacitors (e.g. tantalum, which may even catch fire under reverse voltage conditions) on the regulator's input.

You didn't supply a schematic (and ideally BOM or component ratings/types, if not on the schematic), so it is impossible to be more specific. Close-up photos of the relevant components may also be helpful, in case they show any signs of overheating.

In summary: The regulator could have been partially damaged, which would fit with your result. Any other polarised device (e.g. capacitor) which was exposed to the reversed voltage, might also have been damaged.

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  • \$\begingroup\$ thanks for the detailed answer. I don't have schematics or full BOMs of the circuit, as its a commercial RC receiver. All caps are SMD non-polarized caps. I applied 7.2V with reversed polarity. No component shows signs of excess heat. I will try to replace the LDO and hopefully it works. \$\endgroup\$ – Xaser Aug 2 '16 at 12:38
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    \$\begingroup\$ @Xaser - Hi - If the caps are non-polarised, and the normal input voltage was just inverted as you explain, then I would not worry about those caps. The LDO regulator is the main suspect. Depending on how you wanted to approach this, you could remove the original LDO, remount it on a prototype board with new input & output caps, and test it there. Of course that's lots of work, but that procedure would prove that the original LDO is definitely faulty. In my experience, it is likely to have been damaged by the reverse polarity input, if the circuit has no protection against that. Good luck! \$\endgroup\$ – SamGibson Aug 2 '16 at 12:49

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